Copyright is owned by the Author of the thesis.  Permission is given for 
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Effect of various whey protein supplements 

on recovery from prolonged endurance exercise in 

trained cyclists 

A thesis presented in partial fulfilment of the requirements for the 

degree of 

Master of Science 

in 

Nutritional Science 

at Massey University, Palmerston North, 

New Zealand. 

Dean Mathew Rankin 

2005 



ABSTRACT 

Background: 

Protein-containing recovery beverages are proposed to support an athlete's recovery 

from exercise through stimulation of insulin release, promoting the restoration of 

muscle glycogen stores, and stimulation of protein synthesis and muscle protein 

restoration. 

Objective: 

The present study aimed to determine, (1) whether there is an insulinotropic effect of 

whey proteins, when consumed in addition to carbohydrate, which is assumed to 

enhance muscle glycogen resynthesis and (2) whether a blend of hydrolysate and intact 

protein, when consumed in addition to carbohydrate, will enhance the athlete's recovery 

from exercise. 

Design: 

Twelve trained top level cyclists repeated a protocol on four consecutive weeks, during 

which either a control beverage (Carb) or three beverages containing whey protein 

( carbohydrate and intact protein (Carb + I); carbohydrate and protein hydrolysate (Carb 

+ H; carbohydrate and intact protein : protein hydrolysate mix (Carb + M)) were 

consumed during recovery from exhaustive endurance exercise. The beverages were 

formulated to supply 1.2 g/kg/hour carbohydrate and 0.4 g/kg/hour protein. Subjects 

followed a controlled diet two days before each experimental day. On the experimental 

day the athletes each performed a glycogen-depleting exercise programme, then 

received the designated dietary beverage every 30 minutes for the first two hours post-

exercise. The progress of recovery was monitored via the measurement of 

cardiovascular recovery, and the appearance and relative concentration of metabolites in 

blood (15 samples over a four hour period, obtained via an indwelling cannula) and 

urine samples ( 13 samples over a seven hour period) collected sequentially during the 

post-exercise recovery period. 

Results: 

Plasma albumin concentrations were significantly lower following consumption of 

beverages containing whey protein (Carb + H, p<0.01; Carb + M, p<0.05) compared to 

ii 



that observed with the Carb beverage. Urine output was significantly higher after 

consumption of the Carb beverage than with any of the three-protein containing 

beverages (Carb + I, p<0.01; Carb + H, p<0.05; Carb + M, p<0.05) during the period of 

controlled fluid consumption. Heart rate recovery was found to be significantly greater 

following consumption of the three protein-containing beverages (Carb + I, p<0.001; 

Carb + M, p<0.001, Carb + H, p<O.O l) than following consumption of the Carb 

beverage. The Carb + M beverage produced increased heart rate recovery (p<0.00 l) 

compared to that observed following consumption of the other two protein-containing 

beverages (Carb + I, Carb + H). Following correction of the data for haematocrit, to 

account for the hydration status of the athletes, a significant difference (p<0.05) in the 

ratio of plasma insulin to plasma glucose concentrations was found following 

consumption of any of beverages containing whey protein (Carb + I, Carb + H, Carb + 

M) compared to that observed for the Carb beverage. Consumption of the Carb + I 

beverage resulted in significantly higher concentrations of urinary nitrogen excretion as 

urea (p<0.05) and ammonia (p<0.01), and significantly higher plasma concentrations of 

the amino acids Valine, Leucine, Isoleucine, Phenylalanine, Tryptophan, and Tyrosine 

(p<0.05). 

Conclusions: 

The addition of whey protein to a carbohydrate-containing beverage stimulated 

enhanced recovery from exercise. A major factor in the improved recovery was 

increased rehydration following consumption of the protein-containing beverages, 

mainly due to the high sodium content of these beverages. This increased rehydration 

was shown to influence results for plasma insulin and plasma glucose concentrations 

where, after accounting for the hydration status of athletes, a difference between 

consumption of the Carb beverage and that observed for any of the three protein­

containing beverages was observed. The results also allude to a potential benefit of 

protein hydrolysates over intact protein on protein recovery. Consuming a protein mix 

(Carb + M) also appears to improve heart rate recovery compared to consuming either 

intact (Carb + I) or hydrolysed (Carb + H) proteins individually. The results of this 

study highlight the importance of dietary protein on enhancing recovery from endurance 

exercise. 

iii 



ACKNOWLEDGEMENTS 

I would like to express my sincere appreciation to my supervisors: Dr Alison Darragh 

(for her involvement right throughout this extensive project in all aspects of its 

planning, implementation, analysis and thesis writing); Dr Roger Lentle (for his 

involvement in the experimental trial, statistical analysis and thesis writing); and to 

Associate Professor Hugh Morton for his statistical help during the initial stages of the 

study. Their advice, guidance and encouragement throughout the study was excellent. I 

would also like to thank them for both their patience and their understanding of my 

other commitments outside of this thesis, which prolonged this project. 

I would also like to thank Chris Booth for her time and efforts in the planning and 

implementation of this study, especially the time she put in during the experimental trial 

in the processing of samples. In addition, thanks also to Lena LUckel (from Germany) 

for volunteering her time and effort while in New Zealand to help out both prior to and 

during the experimental trial. 

Thanks also to Fonterra Co-operative Group Ltd for the financial backing to allow this 

trial to occur. Thanks to all those at Fonterra who contributed their time and effort in 

supporting this study, especially Angela Rowan (for her continued support for the study 

both in gaining funding and overseeing it for Fonterra), Arron Harford (for his work 

with the proteins used in this study) and Roxanne Brassington (for her work in the 

masking of the dietary beverages). 

Thanks must also go to all the subjects that participated in this trial. Their willingness 

and outstanding commitment to this trial to ensure its success was greatly appreciated. It 

was great privilege to have such highly talented and committed subjects on this trial. 

I would also like to thank my current employer, Universal College of Leaming (UCOL), 

for their assistance in allowing me to pursue post-graduate study and to the people there 

who, over the years, supported me during my studies. 

iv 



And finally, a very special thanks to my wife, Paula, and two children, Dominic and 

Abby, for all of their patience, support and understanding throughout the entire duration 

of this study. Without your support, completion of this would not have been possible. 

Approval for this research has been obtained from both the Massey University Ethics 
Committee and the Manawatu-Whanganui Ethics Committee for the experiments 

described in this thesis. 

V 



TABLE OF CONTENTS 

ABSTRACT 

ACKNOWLEDGEMENTS 

TABLE OF CONTENTS 

LIST OF TABLES 

LIST OF FIGURES 

LIST OF ABBREVIATIONS 

GENERAL INTRODUCTION 

CHAPTERl LITERATURE REVIEW 

1.1 Introduction 

1.2 Nutritional Strategies During Exercise 

1.2.1 Fluids and Electrolytes 
1.2.2 Carbohydrate 
1.2.3 Protein 

1.3 Nutritional Strategies Post-Exercise 

1.3 .1 Fluids and Electrolytes 
1.3.2 Carbohydrates 
1.3.3 Protein 

1.3.3.1 Protein and the Insulin Response 
1.3 .3 .2 Protein and Protein Synthesis / Degradation 

1.4 Summary / Hypothesis 

CHAPTER2 METHODS 

2.1. Subjects 
2.1.1. Screening of Subjects 

2.2. Experimental Design 
2.2.1. Pre-Experimental Period 

2.2.1.1. Determination of Peak Oxygen Uptake and 
Maximum Power Output 

2.2.1.2. Determination of Body Composition 
2.2.1.3. Sum of Skinfolds 

vi 

Page Number 

ii 

iv 

vi 

ix 

xi 

xvi 

1 

3 

3 

4 

4 
8 

13 

18 

19 
21 
26 
27 
35 

42 

43 

43 
43 

44 
44 

44 
46 
47 



2.2.1.4. Percentage Body Fat 
2.2.1.5. Body Mass Index (BMI) 
2.2.1.6. Waist : Hip Ratio 
2.2.1.7 . Somatotype 

47 
47 
48 
48 

2.2.2. Experimental Design 49 
2.2.2.1. Dietary Beverage Composition 49 

2.2.2.1 .1. Carbohydrate Content of the Dietary 
Beverages 51 

2.2.2.1.2 . Protein Content of the Dietary 
Beverages 51 

2.2.2.1.3 . Anion : Cation Balance 
2.2.2.1.4. Double-Blinding of Treatments and 53 

Administration of the Beverages 54 

2.2.2.2. Experimental Period 
2.2.2.2.1 . Day 1 (Diet Record) 
2.2.2.2.2. Day 2 & 3 (Controlled Diet) 
2.2.2.2.3. Day 4 (Experimental Day) 

2.2.2.2 .3.1. Glycogen Depletion Protocol 
2.2.2.2.4. In-Dwelling Cannulae and Blood 

Sampling 
2.2.2.2.4.1. In-Dwelling Cannulae 
2.2.2.2.4.2. Blood Sampling 

2.2.2.2.5. Urine Sampling 
2.2.2.2.6. Heart Rate Recording 
2.2.2.2.7. Blood Pressure Measurement 
2.2.2.2.8. Snack 

55 
59 
59 
60 
60 

63 
63 
64 
65 
66 
66 
67 

2.3. Chemical Analysis 

2.4 . Statistical Analysis 

68 

69 

CHAPTER3 RESULTS 

3.1 Experimental Trial Overview 70 
3 .1.1 Exercise Protocol 70 
3.1.2 Trial Beverage Consumption 70 
3.1.3 Blood & Urine Sampling 

3.2 Anthropometric and Exercise Test (V02peak and Wmax) Results 71 

3.3 Variability Associated with Chemical Analyses 74 

3.4 Amino Acid Composition of Diets 76 

3.5 Metabolic and Physiological Responses 77 
3.5.1 Rehydration 77 

3 .5 .1.1 Haematocrit 77 
3.5.1.2 Plasma Albumin 79 
3.5.1.3 Urine Production 81 

3.5.1.3.1 Analysis of Cumulative Urine Output 
Over Initial 240 Minutes 81 

3.5.1.3.2 Temporal Pattern of Urine 82 

vii 

70 



3.5.1.3.3 Temporal Pattern of Urine Output 
Over Initial 240 Minutes 

3.5.1.3.4 Temporal Pattern of Urine Output 
Over Full 420 Minutes 

3.5.2 Carbohydrate Metabolism 

3.5.3 Cardiovascular Recovery 
3.5.3.1 Heart Rate 
3.5.3.2 Systolic Blood Pressure 
3.5.3.3 Diastolic Blood Pressure 
3.5.3.4 Pulse Pressure 

3.5.4 Protein Recovery 
3.5.4.1 Urinary 3-methylhistidine 
3.5.4.2 Urinary Urea 
3.5.4.3 Plasma Urea 
3.5.4.4 Urinary Ammonia 
3.5.4.5 Urinary Creatinine 
3.5.4.6 Plasma Essential Amino Acids 
3.5.4.7 Plasma Non-Essential Amino Acids 
3.5.4.8 Plasma Amino Acids Not Supplied in Beverages 

CHAPTER4 DISCUSSION 

4.1 Rehydration 
4.1.1 Plasma Albumin 
4.1.2 Haematocrit 
4.1.3 Urine Output 
4.1.4 Sodium and Rehydration 
4.1.5 Role of Potassium in Supporting Rehydration 
4.1 .6 Comparison of the Protein-Containing Beverages on 

Rehydration 

4.2 Cardiovascular Recovery 

4.3 Carbohydrate Recovery 

4.4 Protein Recovery 
4.4.1 Plasma Amino Acids 
4.4.2 Plasma Urea Concentration and Urinary Excretion of Urea 

and Ammonia 
4.4.3 Proposed Mechanism for Difference Between Intact 

Protein and Protein Hydrolysate Beverages on Protein 
Recovery 

4.4.4 3-Methylhistidine 

CHAPTER 5 CONCLUSIONS & GENERAL 
DISCUSSIONS 

REFERENCES 

viii 

84 

84 

85 

89 
89 
93 
94 
97 

99 
99 

101 
103 
106 
108 
109 
116 
119 

121 

121 
121 
123 
124 
125 
127 

128 

129 

131 

134 
134 

136 

137 
138 

140 

144 



LIST OF TABLES 

Page 
CHAPTER 1 LITERATURE REVIEW Number 

Table 1.1. Endogenous fuel sources in man, (Lambert et al., 1997). 9 

Table 1.2. Summary of research examining the effect of the consumption of protein in 30 
addition to carbohydrate on insulin response and muscle glycogen 
resynthesis. 

Table 1.3. Amino acid composition of hydrolysates of whey, pea and wheat protein, 34 
and intact casein protein (van Loon et al., 2000a). 

Table 1.4. Leucine and Branched Chain Amino Acid (BCAA) content of foods) 40 
(Layman & Baum, 2004). 

Page 
CHAPTER 2 METHODS Number 

Table 2.1. List of proposed performance enhancing substances that have the potential 44 
to influence a subject's carbohydrate and / or protein metabolism if used 
prior to or during a post-exercise recovery study. 

Table 2.2. Body composition assessment sites used in a post-exercise recovery study. 46 

Table 2.3. Ingredient composition of the four dietary beverages powders used in a 50 
post-exercise recovery study. 

Table 2.4. Expected intake rates for both of the dietary beverage powder (grams of dry 50 
matter (DM)) and water, expressed per kg of body weight, used in a post-
exercise recovery study. 

Table 2.5. Typical amino acid composition of ALACEN™ 895 Whey Protein Isolate* 52 
used in a post-exercise recovery study. 

Table 2.6. Mineral composition* of the whey protein isolate and whey protein 53 
hydrolysate used in a post-exercise recovery study. 

Table 2.7. Initial and Final Dietary Electrolyte Balance (DEB) + for the three protein 54 
containing beverages tested in a post-exercise recovery study. 

Table 2.8. Randomised allocation of the four beverages tested used in a post-exercise 58 
recovery study designed so that each beverage does not routinely follow the 
same combination in each subject. 

Table 2.9. Diet composition analysis of the controlled diet consumed the two days 59 
prior to each experimental day in a post-exercise recovery study. 

Table 2.10. Desired water consumption throughout the experimental day in a post- 62 
exercise recovery study. 

Table 2.11. Diagnostic kits used for chemical analysis performed in a post-exercise 68 
recovery study. 

ix 



Page 
CHAPTER 3 RESULTS Number 

Table 3.1. Summary of the data gained from anthropometric assessment of the ten 72 
male subjects that were involved in a post-exercise recovery study. 

Table 3.2. Data from the pre-trial fitness assessment for the 11 males scheduled to be 73 
involved in a post-exercise recovery study. 

Table 3.3. Variability (CV%) associated with various chemical analyses conducted on 74 
samples collected during a post-exercise recovery study. 

Table 3.4. Variability (CV%) associated with the determination of amino acids in the 75 
beverages used in a post-exercise recovery study. 

Table 3.5. Determined amino acid composition of the four dietary beverages, 76 
expressed as g/kg BWT delivered, in a post-exercise recovery study. 

Table 3.6. The mean and standard error for haematocrit (%) of all athletes for the four 78 
beverages during the time period from cessation of exercise to 240 minutes 
post-exercise during a post-exercise recovery study. 

Table 3.7. The mean and standard error of plasma albumin concentration (g/L) for the 80 
response to the four beverages during the time period from cessation of 
exercise to 240 minutes post-exercise in a post-exercise recovery study 

Table 3.8. The mean and standard error of urine output results (g/30minutes) for the 82 
response to the four beverages during the time period from cessation of 

Table 3.9. 

Table 3.10. 

Table 3.11. 

Table 3.12. 

Table3.13. 

Table 3.14 

Table 3.15 

exercise to 420 minutes post-exercise in a post-exercise recovery study. 

Desired and actual water consumption achieved throughout the 
experimental day in a post-exercise recovery study. 

The mean and standard error results of plasma insulin concentration for the 
response to the four beverages during the time period from cessation of 
exercise to 240 minutes post-exercise in a post-exercise recovery study. 

The mean and standard error results of plasma glucose concentration for the 
response to the four beverages during the time period from cessation of 
exercise to 240 minutes post-exercise in a post-exercise recovery study. 

Linear Regression results for heart rate during the post-exercise recovery 
period in a post-exercise recovery study. 

Analysis results of slope coefficients for post-exercise heart rate recovery 
for the response to four dietary beverages during a post-exercise recovery 
study. 

Statistical analysis of the effect of dietary beverages on individual mean 
plasma essential amino acid levels, by pairwise repeated measures 
ANOV A, during the time period from cessation of exercise to 240 minutes 
post-exercise during a post-exercise recovery study. 

Effect of dietary beverages on individual mean plasma non-essential amino 
acid levels, by pairwise repeated measures ANOV A, during the time period 
from cessation of exercise to 240 minutes post-exercise during a post­
exercise recovery study. 

X 

83 

87 

87 

91 

92 

115 

118 



LIST OF FIGURES 

Page 
CHAPTER 1 LITERATURE REVIEW Number 

Figure 1.1. Estimated balance of Na+ intake and Na+ loss during 3 h of exercise at 7 
marathon pace. Note: l mmol of NaCl weighs 58.5 mg (Lambert, et al, 
1997). 

Figure 1.2. Summary of the main pathways of energy metabolism using carbohydrate, 11 
lipid, and protein as energy sources (Maughan et al., 1997, pl6). 

Figure 1.3. Amino acids are degraded to pyruvate, acetate, or to intermediates of the 14 
TCA cycle (Maughan et al., 1997, p124). 

Figure 1.4. Amino acid metabolism in the muscle. (Wagenmakers, 2000, pl20).. 14 

Figure 1.5. Interorgan relationship in the handling of amino acids. Dashed arrow, 16 
prolonged starvation only. (Wagenmakers, 2000, p122) .. 

Figure 1.6. Muscle glycogen synthesis rates are depicted against the rate of 25 
carbohydrate ingestion. The horizontal line depicts the absolute maximum 
for muscle glycogen synthesis (Jentjens & Jeukendrup, 2003). 

Figure 1.7. Rates of leg protein dynamics (a) and whole body protein dynamics (b) for 37 
I O subjects given an oral nutrient supplementation either immediately after 
exercise (EARLY) or 3 h postexercise (LATE). * Significantly different 
(p<0.05), EARLY vs LATE (Levenhagen et al., 2001). 

Figure 1.8. Insulin signalling cascade. GLUT! , insulin independent glucose 40 
transporter; PKC, protein kinase C; eIF, translational initiation factors. 
(Layman & Baum, 2004). 

Page 
CHAPTER 2 METHODS Number 

Figure 2.1. Overview of a seven day experimental period highlighting division of the 56 
two phases for a post-exercise recovery study. 

Figure 2.2. Schematic overview of the Day 4 (Experimental Day) for a post-exercise 57 
recovery study. 

Figure 2.3. Glycogen depletion protocol used in a post-exercise recovery. 61 

xi 



Page 
CHAPTER 3 RESULTS Number 

Figure 3.1. Example graph of V02 output from a pre-experimental trial fitness test. 73 
The five-second interval for determining V02peak is highlighted on the right 
hand side of the graph. The result for this athlete was recorded at 4.73 
L/min or 71.77 ml/kg/min. 

Figure 3.2. Mean (± SEM) haematocrit (%) after ingestion of a control drink 78 
containing carbohydrate only (Carb; n= 10) and drinks containing 
carbohydrate plus either: whey protein hydrolysate (Carb + H; n= 10), intact 
whey protein (Carb + I; n= l l), or 50% whey protein hydrolysate and 50% 
intact whey protein (Carb + M; n=l 1) in a 240 minute period following 
exercise and recovery beverage consumption. 

Figure 3.3. Mean (± SEM) plasma albumin concentrations {g/L) after ingestion of a 80 
control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l 1), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l l) in a 240 
minute period following exercise and recovery beverage consumption. 

Figure 3.4. Mean (± SEM) total urine volumes expressed as ml/kg BWT for the first 81 
240 minutes (fluid intake controlled during this period) in a post-exercise 
recovery study. Similar letter designations implies non-significance, non-
similar implies significance (p<0.05). 

Figure 3.5. Mean (± SEM) urine outputs (g/30minutes) after ingestion of a control 83 
drink containing carbohydrate only (Carb; n=lO) and drinks containing 
carbohydrate plus either: whey protein hydrolysate (Carb + H; n=IO), intact 
whey protein (Carb + I; n=l l), or 50% whey protein hydrolysate and 50% 
intact whey protein (Carb + M; n=l l) in a 420 minute period following 
exercise and recovery beverage consumption. 

Figure 3.6. Mean (± SEM) plasma insulin concentrations (mmol/L) after ingestion of a 88 
control drink containing carbohydrate only (Carb; n= 10) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l 1), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l l) in a 240 
minute period following exercise and recovery beverage consumption. 

Figure 3.7. Mean(± SEM) plasma glucose concentrations (mmol/L) after ingestion of 88 
a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n= lO), iniacl whey protein (Carb + I; n=l l), er 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=JJ) in a 240 
minute period following exercise and recovery beverage consumption. 

Figure 3.8 . Linear regression analysis results of mean post-exercise pulse rate recovery 89 
(bpm) (n=4900) after ingestion of a control drink containing carbohydrate 
only (Carb; n=IO) and drinks containing carbohydrate plus either: whey 
protein hydrolysate (Carb + H), intact whey protein (Carb + I), or 50% 
whey protein hydrolysate and 50% intact whey protein (Carb + M) in a 240 
minute period following exercise and recovery beverage consumption. 

xii 



Figure 3.9. 

Figure 3.10. 

Figure 3.11. 

Figure 3.12. 

Figure3.13. 

Figure 3.14. 

Figure 3.15. 

Figure 3.16. 

Linear regression analysis results of mean post-exercise pulse rate recovery 
(bpm) following consumption of each of the four dietary beverages 
(n=4900): (a) Carbohydrate Only; (b) Carbohydrate and Intact Protein; (c) 
Carbohydrate / Protein Hydrolysate; (d) Carbohydrate and 50% whey 
protein hydrolysate and 50% intact whey protein, in a 240 minute period 
following exercise and recovery beverage consumption. 

Mean(± SEM) systolic blood pressures (mmHg) after ingestion ofa control 
drink containing carbohydrate only (Carb; n=lO) and drinks containing 
carbohydrate plus either: whey protein hydrolysate (Carb + H; n=lO), intact 
whey protein (Carb + I; n=l 1), or 50% whey protein hydrolysate and 50% 
intact whey protein (Carb + M; n=ll) in a 420 minute period following 
exercise and recovery beverage consumption. 

Mean (± SEM) diastolic blood pressures (mmHg) after ingestion of a 
control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l 1), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l l) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean (± SEM) pulse pressure values (mmHg) after ingestion of a control 
drink containing carbohydrate only (Carb; n=lO) and drinks containing 
carbohydrate plus either: whey protein hydrolysate (Carb + H; n=lO), intact 
whey protein (Carb + I; n=l l), or 50% whey protein hydrolysate and 50% 
intact whey protein (Carb + M; n=l 1) in a 420 minute period following 
exercise and recovery beverage consumption. 

Mean (± SEM) urinary 3-methylhistidine excretion (mg) after ingestion of 
a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l 1), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l l) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean (± SEM) urinary urea nitrogen excretion (mg) after ingestion of a 
control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=J l) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean (± SEM) plasma urea concentration (mmol/L) after ingestion of a 
control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l 1), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l l) in a 420 
minute period following exercise and recovery beverage consumpliu1L 

Mean (± SEM) urinary ammonia nitrogen excretion (mg) after ingestion of 
a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l l) in a 420 
minute period following exercise and recovery beverage consumption. 

xiii 

90 

96 

96 

98 

99 

105 

105 

107 



Figure 3.17. 

Figure 3.18. 

Figure 3.19. 

Figure 3.20. 

Figure 3.21. 

Figure 3.22 . 

Figure 3.23. 

Figure 3.24. 

Mean (± SEM) total urinary creatmme nitrogen excretion (mg) after 
ingestion of a control drink containing carbohydrate only (Carb; n=lO) and 
drinks containing carbohydrate plus either: whey protein hydrolysate (Carb 
+ H; n=lO), intact whey protein (Carb + I; n=ll), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=I I) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean (± SEM) plasma Valine concentration (nmol/ml) after ingestion of a 
control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=II) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean(± SEM) plasma Methionine concentration (nmol/ml) after ingestion 
of a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=I I) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean(± SEM) plasma Leucine concentration (nmol/ml) after ingestion of a 
control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=ll), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=I I) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean (± SEM) plasma Isoleucine concentration (nmol/ml) after ingestion 
of a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n= 10), intact whey protein (Carb + I; n= 11 ), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=J I) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean (± SEM) plasma Phenylalanine concentration (nmol/ml) after 
ingestion of a control drink containing carbohydrate only (Carb; n= 10) and 
drinks containing carbohydrate plus either: whey protein hydrolysate (Carb 
+ H; n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M ; n=I I) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean(± SEM) plasma Tryptophan concentration (nmol/ml) after ingestion 
of a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H ; 
n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M ; n=I I) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean(± SEM) plasma Lysine concentration (nmol/rnl) after ingestion of a 
control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M ; n=II) in a 420 
minute period following exercise and recovery beverage consumption. 

xiv 

108 

111 

111 

112 

112 

113 

113 

114 



Figure 3.25. 

Figure 3.26. 

Figure 3.27. 

Figure 3.28. 

Mean (± SEM) plasma Arginine concentration (nmol/ml) after ingestion of 
a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l 1), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l 1) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean (± SEM) plasma Tyrosine concentration (nmol/ml) after ingestion of 
a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l l) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean(± SEM) plasma omithine concentration (nmol/ml) after ingestion of 
a control drink containing carbohydrate only (Carb; n=lO) and drinks 
containing carbohydrate plus either: whey protein hydrolysate (Carb + H; 
n=lO), intact whey protein (Carb + I; n=l l), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=l 1) in a 420 
minute period following exercise and recovery beverage consumption. 

Mean (± SEM) plasma 3-methylhistidine concentration (nmol/ml) after 
ingestion of a control drink containing carbohydrate only (Carb; n=lO) and 
drinks containing carbohydrate plus either: whey protein hydrolysate (Carb 
+ H; n=lO), intact whey protein (Carb + I; n=ll), or 50% whey protein 
hydrolysate and 50% intact whey protein (Carb + M; n=JJ) in a 420 
minute period following exercise and recovery beverage consumption. 

xv 

117 

117 

120 

120 



Carb 

Carb + H 

Carb + I 

Carb + M 

ACSM 

ADA 

ANP 

BWT 

DEB 

DM 

DOC 

GLUT 

FAO 

ISAK 

TCA 

UNU 

V02peak 

Wmax 

WHO 

LIST OF ABBREVIATIONS 

Carbohydrate Only 

Carbohydrate+ Whey Protein Hydrolysate 

Carbohydrate + Intact Whey Protein 

Carbohydrate+ 50% Whey Protein Hydrolysate + 50% Intact 
Whey Protein 

American College of Sports Medicine 

American Dietetic Association 

Atrial Natriuretic Peptide 

Body Weight 

Dietary Electrolyte Balance 

Dry Matter 

Dietitians of Canada 

Glucose Transporter Carrier Proteins 

Food and Agriculture Organization of the United Nations 

International Society for the Advancement of Kinanthropometry 

Tricarboxylic Acid 

United Nations University 

Peak Oxygen Uptake 

Maximum Power Output 

World Health Organisation 

xvi 



GENERAL INTRODUCTION 

Athletes around the world continually strive for that elusive edge that will give them 

victory over their fellow competitors. This search for the perfect performance is 

epitomised by the foundations of the modem Olympic Games and Olympism. The 

International Olympic Committee defines Olympism as . .. 

II a philosophy of life, exalting and combining in a balanced whole the 

qualities of body, will and mind. Blending sport with culture and education, 

Olympism seeks to create a way of life based on the joy found in effort, the 

educational value of good example and respect for universal fundamental 

ethical principles." (International Olympic Committee, 2004, p. 9) 

An athlete's performance is influenced by a multitude of factors, ranging from their 

genetic makeup and their physical fitness, through to motivational levels and the desire 

to succeed. Nutrition is another such factor which, while a relatively new science in 

terms of sports nutrition, now has a strong focus within the sport science research 

community. With the commercialism of sport, athletes have a lot to gain from the 

spoils of victory, ranging from the personal satisfaction gained years of training and 

effort, through to financial rewards. This has led to the development of a 'win at all 

costs' attitude, which has often taken athletes down the path of performance enhancing 

ergogenic aids, many of which are banned by the International Olympic Committee and 

the World Anti-Doping Agency. With nutrition, however, there are many dietary 

factors that have the potential to provide the athlete with an ergogenic, or performance­

enhancing effect. Dietary protein definitely falls into this category, and its potential has 

recently been further enhanced through the development of manufacturing processes 

which produce protein forms that are well suited to an athletes physiological needs. 

While protein intake is traditionally associated with strength-based athletes, it is now 

evident that the protein requirement of endurance athletes is also increased due to a 

combination of exercise-induced muscle damage and the use of protein as a fuel source. 

1 



Throughout history, athletes have trialled nutritional strategies, focused on dietary 

protein, that have resulted in both in enhancement and detriment of athletic 

performance. One of the most famous accounts of food consumption relates to Milos, a 

five-time Olympic Cretan wrestler champion (552-516 B.C.), who had a reported daily 

meat intake of 10kg per day (Maughan & Burke, 2000). Following the 1936 Berlin 

Olympics, it was stated that athletes frequently focused on the intake of meat and on 

average took in nearly half a kilogram of meat per day, with pre-event meals consisting 

of steak and eggs, supplemented with meat-juice (Schenk, 1936, cited in McArdle, 

Katch & Katch, 1999). This large consumption of protein by athletes, in the form of 

meat, has more recently been replaced with specially formulated protein supplements, 

which provide the athlete with a more convenient and healthier option. 

Dietary protein supplementation is now common place both amongst athletes and the 

wider population, with a focus related to both exercise and weight loss. It also 

represents a major part of a world-wide, multi-million dollar supplement industry. In 

relation to athletes, there is a common belief that protein consumption has significant 

benefits on both performance and recovery from exercise. Yet uncertainty still remains 

with regard to the best form of dietary protein to use and when is the optimal time for its 

consumption (generally related to an exercise session). To date, nutritional research has 

been focused around both pre-exercise and during exercise nutritional strategies for 

maximising performance. However, due to the demands of modem sport, nutritional 

strategies focused on maximising recovery from exercise are of increased importance. 

It is during this post-exercise recovery period that the true benefits of protein 

consumption are becoming more evident. The potential benefit of protein to the 

recovering athlete relates to achieving maximal training adaptations, in addition to 

ensuring that exercise performance is not impaired due to any lingering effects from a 

previous exercise session. 

There is still a lot to learn about the true extent that dietary protein intake may have on 

the recovering athlete. This study looks to extend the current knowledge related to the 

effect of dietary protein in exercise recovery, with a focus on the use of different forms 

of whey protein (intact and hydrolysed) on post-exercise recovery of endurance athletes. 

2 



1.1 INTRODUCTION 

Chapter 1 

LITERATURE REVIEW 

There is no doubt that exercise places the human body under a large amount of stress. 

The demands of exercise necessitate maintenance of normal body homeostasis, while 

ensuring the working muscles receive an adequate blood supply. The nature of 

endurance exercise means that the body must try to maintain homeostasis over a 

prolonged period while the athlete pushes themselves to their physical limits. In the 

past, most research has focused on optimising nutritional practices before and during 

exercise with little emphasis placed on the post-exercise recovery phase. Due to the 

demands of modem sport, however, the importance of maximising an athlete ' s recovery 

from exercise is receiving greater recognition. Many athletes are in a situation where 

they compete in multiple events throughout the competitive season, in addition to the 

demands of their high training levels. The faster an athlete recovers from one bout of 

exercise the better able they will be to cope with subsequent exercise bouts. If an 

athlete does not complete their recovery they will find themselves beginning exercise in 

an already depleted state, which will limit athletic performance. Selection of an optimal 

nutrition programme for recovery will depend on the type of exercise ( e.g. resistance, 

high intensity I anaerobic, or endurance exercise) they have been performing. The 

focus of this review will be on the metabolic and nutritional aspects of recovery from 

endurance exercise in man and nutritional strategies for maximising the rate of 

recovery. 

3 



1.2 NUTRJTIONAL STRATEGIES DURING EXERCISE 

In order to understand the important nutritional strategies relevant for an athlete's 

recovery it is necessary to understand the effect exercise has on an athlete's 

metabolism. For the purposes of this review, this will be discussed in three sections: 

Fluids and Electrolytes; Carbohydrate; and Protein. 

1.2.1 . FLUIDS & ELECTROLYTES 

During exercise, the metabolic heat that is produced must be dissipated in order 

to prevent hyperthermia. Sweating is the major mechanism for heat loss, with 

as much as 75% of the heat lost during exercise achieved via this mechanism 

(Hargreaves, 2000). Sweat rates vary widely between individuals and between 

different modes of exercise, with environmental conditions also imparting a 

significant effect. Rates of sweating increase when either heat production is 

accelerated through an increase in metabolic rate, or heat loss via evaporation is 

decreased by a hotter, more humid or less windy environment (Dennis et al., 

1997). In hot, dry environments, evaporation of sweat accounts for more than 

80% of metabolic heat loss (American College of Sports Medicine, American 

Dietetic Association & Dietitians of Canada, 20001). It could be expected that 

an endurance cyclist may lose between 1.0-1.25 kg Body Weight (BWT)/hour 

under normal conditions, with endurance runners expecting to lose between 

1.0-1.7 kg BWT/hour (Rehrer & Burke, 1996; Dennis et al., 1997), with the 

majority of this weight loss being fluid lost through sweating. This is a 

significant decrease in body weight, especially as performance has been shown 

to decrease following fluid loss of approximately 1-2% loss of body weight 

(Sawka et al., 2000). In the advanced stages of dehydration, an increase in 

serum sodium concentration and osmolality has been shown to cause a 

reduction in skin blood flow and sweating (Dennis et al., 1997). Although fluid 

1 Herewith ACSM, ADA & DOC (2000). 

4 



consumption may limit the rise in serum osmolality and maintain sufficient skin 

blood flow for maximum heat loss, it will not prevent dehydration from 

occurnng. 

During endurance exercise, the athlete's requirement to replace fluids, along 

with maintaining a supply of glucose to the body, has led to the development of 

carbohydrate-based sports drinks. The general recommendation during exercise 

is for the carbohydrate content of any drinks consumed to be lower than 10% 

when water absorption is a priority (Coombes & Hamilton, 2000). The two 

major reasons for this relate to the effect carbohydrate content has on gastric 

emptying rate, and the osmolality of the drink. In a study by Noakes et al. 

( 1991 , cited in Coombe & Hamilton, 2000) it was reported that solutions 

containing up to 8% carbohydrate appear to have little effect on the rate of 

gastric emptying. Similarly, it is known that carbohydrate concentration 

influences the amount of water in the small intestine. Thus, when the 

carbohydrate concentration is greater than l 0%, fluid enters the intestine from 

the vascular space (a phenomenon called reverse osmosis), which may promote 

dehydration (Gisolfi & Duchman, 1995; Maughan & Leiper, 1999). A negative 

correlation has been reported between osmolality of luminal contents and water 

absorption (Coombes & Hamilton, 2000). Hypertonic solutions ( osmolality 

greater than that of body fluid) will result in a decrease in water absorption in 

the intestines with a greater secretion of water into the gastrointestinal lumen, 

which in tum may enhance the risk of dehydration. Therefore, both isotonic or 

hypotonic solutions can promote fluid absorption from the intestine. In the 

past, carbohydrate-based beverages usually contained a combination of glucose 

and fructose. The development of synthetic polymer maltodextrins, also known 

as glucose polymers, now allows for the manufacture of beverages with higher 

carbohydrate concentrations, because they allow carbohydrate content to be 

increased without a resultant increase in osmolality (Coombes & Hamilton, 

2000). In a review by Jeukendrup & Jentjens (2000) of the oxidation rate of 

different types of carbohydrate during exercise it was evident that fructose 

5 



appeared to be oxidised at relatively low rates (approximately 25% lower 

oxidation compared with glucose) whereas glucose, sucrose, maltose, 

maltodextrin and soluble starch tended to be oxidised at relatively high rates 

during exercise (approximately lg/min). Galactose was also stated as being 

oxidised at low rates similar to fructose. However, only one study, by Leijssen 

et al. (1995, cited by Jeukendrup & Jentjens, 2000) had been done on galactose 

at this time. Due to the different transport mechanisms available for different 

types of carbohydrates across the intestinal wall, Shi, et al. (1995, cited in 

Jeukendrup & Jentjens, 2000) suggested that the inclusion of different 

carbohydrates in a beverage may increase b9th water and carbohydrate 

absorption despite an increase in osmolality. Recent research has confirmed the 

use of carbohydrate mixes with the oxidation rates of either ( 1) a 

glucose/fructose mix (Jentjens, et al., 2004a) or (2) a glucose/sucrose mix 

(Jentjens, et a., 2004b) found to be higher (approximately 1.25-1.3 g/min), than 

that found following consumption of glucose alone. 

The volume of the fluid consumed is also an important factor in determining the 

rate of gastric emptying, regardless of the composition of the ingested fluid 

(Maughan & Leiper, 1999). As the volume of fluid in the stomach increases, 

the stomach stretches up to a certain point. When maximal distension is 

reached, the pressure inside the stomach increases with the resultant rate of 

gastric emptying increasing initially and then decreasing as the volume is 

reduced (Jeukendrup & Gleeson, 2004). Therefore, a greater volume of fluid in 

the stomach may offset, to some degree, the effects on gastric emptying of 

consuming beverages with higher osmolality. 

During endurance exercise there is also the potential for sodium losses through 

sweat to be significantly greater than the athlete's ability to replace it through 

food or fluid intake (Figure 1. 1). The mechanism for this increased loss during 

exercise is that although sweat glands reabsorb sodium by active transport, their 

ability to reabsorb sodium does not increase in line with an increase in sweat 

6 



rate (Sawka et al., 2000). Therefore, at high sweat rates the concentration of 

sodium in sweat increases. This has significant implications for the athlete 

because with its osmotic drive, sodium plays an important role in the 

distribution of fluids throughout the body. 

The recommendation for athletes to replace large amounts of fluids during 

exercise has given rise to a new problem known as 'hyponatraemia' (also 

referred to as 'water intoxication'). Hyponatraemia is a disorder in fluid­

electrolyte balance which results from an abnormally low plasma sodium 

concentration (Murray et al., 2003). In general, a significant consumption of 

water, and potentially dilute sports drinks, can act to dilute the body's sodium 

concentration, a situation that may be potentially fatal as in the case of 

hyponatraemic encephalopathy (Noakes, 2003). 

Maximum Na+ intake 
over 3 h or exercise 

iat20mEq1· 1 x 1.51. 
which Is• 1.8 g NaCl Typical sweat Na+ losses 

over 3 h ol exercise 
are±60 mEq 1·1 x 31, 
which is~ 10 g NaCl 

Figure 1.1. Estimated balance of Na+ intake and Na+ loss during 3 h of exercise at marathon 

pace. Note: l mmol of NaCl weighs 58 .5 mg (Lambert, et al, 1997). 

Despite the caution required when replacing fluids during exercise, the fact 

remains that consumption of fluids containing carbohydrate and sodium, as 

opposed to consuming solids, is vital as evidenced by the redistribution of 

7 



blood flow that occurs during exercise. During exercise, there is an increase in 

blood flow to the heart and working muscles, with a significant decrease to 

relatively inactive organs such as non-exercising muscles, skin, kidneys, and 

splanchnic organs (McAllister, 1998). Therefore, with this decrease in blood 

flow to the stomach and intestines, an athlete's ability to cope with concentrated 

fluids or solid foods decreases during exercise, and consumption of these may 

potentially lead to gastrointestinal distress. Splanchnic and renal blood flows 

have been found to be reduced in proportion to relative exercise intensity 

(McAllister, 1998). It appears, however, that splanchnic and renal blood flows 

were reduced by less during acute exercise following a period of endurance 

training (McAllister, 1998). Interestingly, this appears to suggest the 

adaptations to endurance training may also increase an athlete's tolerance to 

fluids and foods during exercise. 

Following endurance exercise, the athlete will, to some extent, be in a 

dehydrated state. Correction of this dehydrated state must take into 

consideration the athlete's continued fluid loss following exercise and that 

sodium may also be required to aid in fluid absorption, fluid balance, and 

prevention of hyponatraemia. Inclusion of nutrients in a recovery beverage, 

namely carbohydrate and protein, is also important for stimulating carbohydrate 

and protein recovery as soon possible following cessation of exercise. 

1.2.2. CARBO HYDRA TE 

The importance of carbohydrate as an energy source during endurance exercise 

is emphasised by the reported link between muscle glycogen depletion and 

early fatigue (Dennis et al., 1997). In response to this, and the body's limited 

ability to store carbohydrates compared to fat and protein (Table 1.1 ), strategies 

have been developed to maximise carbohydrate stores and to ensure that 

carbohydrate supply for energy metabolism is maintained for longer during 

8 



endurance exercise. The body normally has sufficient energy stored as fat (as 

adipose tissue and within muscle) to exercise for extended periods of time 

(Table 1.1 ), meaning that the amount of energy stored as fat is not likely to be a 

liming factor in endurance exercise. One of the body's main adaptations to 

endurance exercise is an increased ability to utilise fat for energy and, therefore, 

preserve carbohydrate (Dennis, et al. ( 1997). This type of adaptation is 

beneficial due to the normally abundant stores of fat in our bodies and the 

potential sparing effect on carbohydrate use for energy during exercise. 

Table 1.1. Endogenous fuel sources in man, (Lambert et al., 1997). 

Approximate fuel reserve Estimated days for which store 
would provide energy (n) 

Tissue fuel store g Kl Starving Walking Running 

Adipose Tissue 9000 337 OOO 34.00 10.80 3.85 

Glycogen (liver) 90 1 500 0 .15 0.05 0.02 

Glycogen (muscle) 350 6 OOO 0 .60 0.20 0.07 

Triacylglycerol (muscle) 400 15 048 1.50 0.48 0.17 

Glucose (blood) 20 320 0.03 0.01 >0.01 

Protein 8800 150 OOO 15.00 4.80 1.29 

'Carbohydrate loading' before exercise is designed to increase carbohydrate 

stores to levels above that normally present in an athlete through a combination 

of a high carbohydrate diet (>70% of total energy from carbohydrate) and the 

tapering of exercise in the days prior to competition. Maximising carbohydrate 

stores prior to exercise may increase time to fatigue by extending the time taken 

to deplete muscle glycogen stores during exercise. The ingestion of 

carbohydrates before and during exercise does increase overall reliance on 

carbohydrate oxidation, even at low exercise intensities (50-55% V02peak) 

(Lambert et al., 1997). This could be counterproductive in reducing 

carbohydrate sparing, although this increase should be offset by the resultant 

9 



increase in carbohydrate stores and an increased ability to maintain exercise at 

higher intensities. 

During exercise, the consumption of a carbohydrate-based sports drink, 

normally containing a glucose-maltodextrin mix, is used in order to maintain 

the supply of carbohydrates to the working muscle. Current recommendations 

are for endurance athletes to consume between 40-60 grams of carbohydrates 

per hour of exercise (ACSM, ADA & DOC, 2000). 

Glucose can be stored as liver glycogen or as muscle glycogen (Table 1). The 

main role of liver glycogen is to maintain a stable blood glucose level, for once 

glucose enters the muscle it is effectively trapped through phosphorylation to 

glucose-6-phosphate (Jentjens & Jeukendrup, 2003). Glucose transport into 

skeletal muscle occurs primarily via facilitated diffusion using glucose 

transporter carrier proteins (GLUT). While there are different forms of this 

GLUT transporter, it appears that in the cell membrane of adult muscle fibres 

only the GLUT-4 isoform is expressed in significant levels, indicating its 

importance in glucose uptake (Gaster et al., 2000). Translocation of GLUT4 

transporters from the intracellular pool to the plasma membrane occurs in 

response to stimulation from insulin and/or muscle contraction (Ryder et al., 

2001 ). The effect of these two stimulating mechanisms on muscle glucose 

uptake appears to be additive. Carbohydrate ingestion during exercise 

decreases the conversion of liver glycogen to glucose, thus sparing liver 

glycogen and preventing the risk of hypoglycaemia occurring late in exercise as 

glycogen stores become depleted. However, it does not measurably slow the 

rate of muscle glycogen utilisation until muscle glycogen concentration falls 

below 70 mmol.kg·1 (Lambert et al. , 1997). Sparing liver glycogen may aid in 

delaying the onset of fatigue due to the role of liver glycogen in maintaining 

blood glucose levels during the latter stages of endurance exercise, and as a 

result, also ensure an ongoing supply of glucose to the working muscle for 

energy. 

10 



During exercise, energy is produced from glucose via glycolysis. Carbohydrate 

may be involved in both anaerobic and aerobic metabolic pathways. In 

glycolysis, glucose-6-phosphate is either derived from glycogen or glucose and 

is broken down to lactate under anaerobic conditions and pyruvate under 

aerobic conditions (Maughan et al., 1997). There is an inherent benefit in 

gaining glucose-6-phosphate from glycogen due to the conversion of glucose to 

glucose-6-phosphate requiring the use of an ATP molecule. The pyruvate 

produced from glycolysis can then be converted to Acetyl CoA and completely 

oxidised through the TCA cycle under aerobic metabolism. The interaction in 

metabolism of the three energy yielding substrates ( carbohydrate, lipid and 

protein - Figure 1.2) shows that the hydrolysis of lipids or the catabolism of 

protein, mainly under aerobic conditions, are also important energy sources 

during exercise. While each of these energy substrates provides energy for the 

exercising muscle, the predominant use of one energy substrate during exercise 

will act to decrease the use of the other. 

! fatty acids + glycerol ! 

t t 

· 1 carbohydrates ! ! proteins ! - --1,,_,,,1 /LL!l 
~alanine I j ammonia 

pyruvate I 1 
j L lactate glycine 

urea 

/cetoacetate 

'-------+-- acetyl CoA ______ _, 

\ L__. ketone bodies 

~ 
""-~~ 

glutamate 

I 

Figure 1.2. Summary of the main pathways of energy metabolism using carbohydrate, lipid, 

and protein as energy sources (Maughan et al. , 1997, p16). 

11 



During endurance exercise, the greater an athlete's ability to utilise fat at higher 

intensities of exercise the more muscle glycogen stores will be spared (Dennis 

et al., 1997). Key adaptations to endurance exercise training act to increase the 

contribution of fat to oxidative energy metabolism, with a corresponding 

decrease in the contribution of carbohydrate, during submaximal exercise. 

Factors that may contribute to this adaptive response are increased density of 

mitochondria in skeletal muscle, proliferation of capillaries within skeletal 

muscle ( enhances fatty acid delivery to muscle and oxygen supply for aerobic 

metabolism), an increase in carnitine transferase (facilitates uptake of fat into 

mitochondria), and an increase in fatty acid binding proteins to enhance fatty 

acid transport (Horowitz & Klein, 2001 ). In addition, the activity of lipid­

mobilising and lipid-metabolising enzymes are also increased, such as the 

activity of lipoprotein lipase in the capillary endothelium of trained muscle and 

an enhanced capacity for beta-oxidation of free fatty acids within the 

mitochondria (Maughan, et al., 1997). However, one of the main problems 

associated with the utilisation of lipid as a fuel source is not the physical 

availability of fat, but the rate at which it can be taken up and oxidised by the 

muscle. This limitation effectively means fat oxidation can only supply A TP at 

a rate sufficient to maintain exercise at an intensity of about 65% V02max, with 

fat oxidation being suppressed at higher intensities (Horowitz & Klein, 2000). 

In order to maintain exercise at higher intensities, carbohydrate must be 

utilised. Because of this, depletion of the body's carbohydrate stores will 

increase reliance on lipid to fulfil the energy demands of exercise, leading to a 

forced decrease in exercise intensity and athletic performance. 

Carbohydrate intake before and during endurance exercise will aid in 

maintaining carbohydrate availability for the working muscle and as a result 

should support sustained exercise intensity. Regardless of what strategy the 

athlete employs before and during exercise, however, the athlete will usually 

complete their competition with depleted carbohydrate stores, making 

12 



carbohydrate replacement a key nutritional requirement during post-exercise 

recovery. 

1.2.3. PROTEIN 

During endurance exercise, there is an increase in the use of protein as an 

energy source, mainly towards the end of exercise when carbohydrate stores 

become depleted. It is estimated that protein may provide, through 

gluconeogenic pathways, between 3-6% of the total energy expenditure for 

contracting muscles, depending on the athlete 's nutritional state (Hargraves & 

Snow, 2001). There may be cases where the energy contribution of amino 

acids is higher, perhaps up to 10%, when, for example, initial carbohydrate 

stores are low or when stores are depleted during exercise (Gibala, 2001 ). 

The carbon skeletons of the glucogenic amino acids contribute to glucose 

synthesis through gluconeogenesis (synthesis of glucose from non-carbohydrate 

sources) (Maughan et al. , 1997). Amino acids can also be metabolised to either 

pyruvate or to intermediates of the TCA cycle and used for either glucose 

synthesis or metabolised for energy (Figure 1.3). The liver has the ability to 

oxidise most of the 20 amino acids while human skeletal muscle can only 

oxidise six, which are the three branched chain amino acids (leucine, isoleucine 

and valine), glutamate, aspartate and arginine (Figure 1.4). The involvement of 

amino acids in energy metabolism during exercise is not only as a direct fuel 

for energy production but also as a precursor for the synthesis of TCA-cycle 

intermediates and glutamine (Wagenmakers, 2000). 

13 



alanine 

cysteine 
glycine 

arginine 
histidlne 
glutamine 
proline 

./ 
serine glutamate 
threonine ~ ( 

'\ isocitrate a-ketoglutarate 
pyruvate / \ isoleucine 

leucine \ succinyl CoA- methionine 
isoleucine - acetyl CoA - citrate + valine 
tryptophan / \ succinate 

acetoacetyl CoA / 
( tyrosine 

oxaloacetate fumarate +-- h 
1 1 

. 
! '-._ / p enyaanme 

./ malate 

phenylalanine 
tyrosine 
leucine 

lysine 

tryptophan 

aspartate 
asparagine 

Figure 1.3. Amino acids are degraded to pyruvate, acetate, or to intermediates of the TCA 

cycle (Maughan et al., 1997, pl24). 

Asparagine Leucine X a-KGX lsoleucine 

t---A-ce_:.-~ ... ::...,o_A~MV 
">-{ 

lsoleucine a-KMV 

' 
a-KIV 

Trlcarboxyllc acid 
cycle 

a-ketoglutara~A/anine 

Sourc:?H3,mate Pyrrate 

l Glycogen 
Glutamlne or glucose 

Figure 1.4. Amino acid metabolism in the muscle. (Wagenmakers. 2000, p120) .. 

14 



A key consideration in the metabolism of amino acid carbon skeletons for 

energy is how the muscle metabolises the remaining nitrogen-containing amino 

groups. As shown in Figure 1.5, the amino group of all six amino acids within 

muscle can be removed from the muscle as either alanine or glutamine 

(Wagenmakers, 2000). Within the glucose-alanine cycle, pyruvate used for 

alanine production is derived from either glycolysis or other muscle protein 

derived amino acids. Alanine is then released into the blood and converted to 

glucose via gluconeogenesis in the liver. Formation of glutamine within the 

muscle also provides a mechanism for the muscle to maintain low ammonia 

levels. Ammonia is captured as amide nitrogen in glutamine and provides a 

non-toxic carrier of ammonia from the muscle, through the blood, to be 

excreted as urinary urea (Wagenmakers, 2000). The majority of the nitrogen 

resulting from degradation of amino acids ends up as urea, which is classed as 

metabolically inert, and can be excreted by the kidneys without altering the 

acid-base balance (Maughan, et al., 1997). 

15 



Glucose -----+---- Glucose ----Cl~~\ 
Pyruvate 

Protein ~ 

-----• Alanine 

Leu - --NH 
/le i ------... 

Val /Glutamine 

: - C-skeleton J Glutamine,,~ 

',, Fuel for gut and immune system 
',,,, Precursor DNA/RNA 

-Ammonia 

Non-metabolized 
amino acids 

',,, ... , 

', 

Glucose •------------

Ammonia 

Figure 1.5. Interorgan relationship in the handling of amino acids . Dashed arrow, prolonged 

starvation only. (Wagenmakers, 2000, pl22) .. 

The metabolism of protein for energy during endurance exercise is evidenced 

by an increased rate of branched-chain amino acid (leucine, isoleucine and 

valine) oxidation_ When there is a reduced availability of glucose and free fatty 

acids in the blood during exercise, leucine oxidation increases markedly 

(Rennie & Tipton, 2000; Hargreaves & Snow, 2001 ). This suggests that 

although the use of leucine as a fuel source is important during exercise, its use 

can be suppressed by the use of other fuel sources ( carbohydrate and lipids) if 

sufficient amounts of these other fuels are available. 

The measurement of protein synthesis and protein breakdown during exercise is 

inherently difficult due to the dynamic nature of these metabolic processes, and 

literature available on the effect exercise has on protein metabolism is often 

16 



conflicting. If exercise is intense enough and/or long enough, there is some 

suggestion that protein synthesis will decrease and concurrently protein 

breakdown will increase during exercise (Rennie & Tipton, 2000). A reported 

increase in leucine oxidation during exercise, resulting in a negative net leucine 

balance, certainly suggests an increase in net protein breakdown (Tipton & 

Wolfe, 1998). While protein breakdown may increase during exercise it 

appears that urea production is not elevated, indicating that increased protein 

breakdown during exercise should provide a source of amino nitrogen for later 

use in protein synthesis (Tipton & Wolfe, 1998). 

Supplying dietary protein during exercise is generally not recommended due to 

the demands placed on the gastrointestinal tract for its digestion and absorption. 

Thus an athlete competing endurance exercise is likely to be in a state of net 

protein breakdown. Minimising protein breakdown and stimulating protein 

synthesis through nutritional strategies will enhance the athlete's recovery 

following exercise. 

17 



1.3 NUTRITIONAL STRATEGIES POST-EXERCISE 

A combination of substantial training outputs of endurance athletes, together with the 

demands of their intensive competition season, necessitates the maximisation of 

recovery to ensure the athlete can meet their future exercise demands. According to 

Burke (2000), nutrition-related issues for recovery from exercise include: 

a. Replacement of fluid and electrolytes lost in sweat; 

b. Restoration of muscle and liver glycogen stores; 

c. Regeneration, repair and adaptation processes following the catabolic stress and 

damage caused by the exercise. 

Fluid replacement following exercise is accepted as an important nutritional practice in 

order to correct for fluid lost during exercise. Post-exercise nutrition research has also 

extensively focused on carbohydrate replacement and its effect on the recovery of the 

athlete through muscle glycogen resynthesis. However, the importance of protein on 

the recovery of an athlete is now being recognised particularly for the athlete who is 

going to compete in the near future. Priority must be given to prompt restoration of 

circulating fluid volume and this may be a case for restoring circulatory fluid volume 

prior to intracellular fluid volume. 

18 



1.3.1. FLUIDS & ELECTROLYTES 

Often fluid replacement in athletes is linked inextricably with carbohydrate 

replacement due to the effect carbohydrate intake can have on water absorption. 

Moreover, a recovery beverage containing carbohydrate will fulfil the athlete ' s 

requirement for recovery from dehydration and immediate replenishment of 

muscle and liver carbohydrate stores. As such it is difficult to discuss these as 

separate strategies. However, specifically for fluid replacement, the 

consumption of volumes equal to sweat losses has been found to result in only 

50-70% rehydration, based on body weight restoration, over 2-4 hours of 

recovery (Burke, 2000). This finding may be partially due to sodium losses and 

the limited amount of sodium replaced, because sodium replacement is 

inherently linked to water replacement and rehydration. Nevertheless, it is 

recommended that athletes consume up to 150% of the weight loss during an 

exercise session in order to recover from losses through sweat and obligatory 

urine production (ACSM, ADA & DOC, 2000). 

It is also recommended that the recovery beverage contains some form of 

sodium in order to replace losses incurred during exercise through sweating and 

to reduce the risk of hyponatraemia that may occur if only water is consumed. 

Sodium also aids the rehydration process by maintaining plasma osmolality and 

therefore the athlete's desire to drink (ACSM, ADA & DOC, 2000). 

While it is important to replace fluids post-exercise especially as fluid loss 

continues after exercise has ceased, the risk of dehydration occurring is 

decreased due to reduced metabolic heat production and, as a result, a decreased 

activity of the mechanisms for thermostatic control, such as sweating. While 

increasing the carbohydrate content of a beverage (to greater than 10%) has 

been shown to increase carbohydrate availability, as discussed in previous 

section, it is generally not recommended during exercise as the higher 

carbohydrate content may decrease water absorption (Coombes & Hamilton, 

19 



2000). However, during the post-exercise recovery period, a beverage 

containing a higher carbohydrate concentration may be suitable due to the 

decreased risk of dehydration. 

Decreased unne production occurs following exercise, most likely due to 

dehydration, but due to the redistribution of blood flow that occurs during 

exercise. During exercise, the magnitude of reduction in splanchnic and renal 

blood flows appears to be directly related to relative exercise intensity 

(McAllister, 1998). Renal sympathetic nerve activity may be a mechanism for 

increased angiotensin II through greater release of renin from the kidneys 

(McAllister, 1998). The result of these mechanisms would be a reduction in 

urine production during exercise, which continues during the early stages of 

recovery as the body redistributes blood flow and acts to maintain plasma 

volume. With the redistribution of blood flow back to the kidneys following 

exercise, possibly due to the reduced sympathetic drive, urine production will 

increase as waste products from energy and muscle metabolism are cleared 

from the body. The results of a study by Neumayr et al., (2003) suggested that 

reduced renal perfusion is the mechanism responsible for slight impairment of 

renal function following exhaustive marathon cycling (in the absence of 

systemic dehydration and significant muscle damage). This seemed to be the 

result of stress-induced sympathetic overdrive responsible for the redistribution 

of blood flow during exercise. Neumayr et al., (2003) also highlighted, 

however, that in well-hydrated athletes the high demands of marathon cycling 

only influenced renal function on a minimal scale. 

20 



1.3.2. CARBO HYDRA TES 

Replenishment of carbohydrate stores depleted during exercise occurs mainly 

via ingested carbohydrate, although there is some contribution from 

gluconeogenic pathways (Jentjens & Jeukendrup, 2003). As discussed 

previously, glucose transport into skeletal muscle primarily occurs via 

facilitated diffusion, in response to insulin or muscle contraction, using a 

GLUT4 isoform of the glucose transporter carrier proteins (Kuo et al., 1999). 

Supplying carbohydrates as part of a recovery beverage fulfils an athlete's 

requirement for the replacement of both energy and fluids. In terms of an 

athlete's ability to tolerate carbohydrates following exercise, the redi stribution 

following exercise of blood flow back towards the splanchnic and renal organs 

will increase an athlete's ability to tolerate higher carbohydrate concentrations 

compared to during exercise. The inclusion of carbohydrates in a recovery 

beverage is important to ensure sufficient supply of glucose for muscle 

glycogen synthesis, via increased muscle glycogen synthesis rates following 

exercise. In a review by Jentjens & Jeukendrup (2003) low rates of muscle 

glycogen synthesis were observed when no carbohydrate was ingested after 

exercise (7-12 mmol/kg dry weight (dw)/h), whereas when a carbohydrate 

supplement is taken immediately following exercise the rate appears to be in 

the range of 20-50 mmol/kg dw/h. 

The pattern of muscle glycogen synthesis following glycogen depleting 

exercise appears to occur in a biphasic manner with rapid and slow phases 

(Jentjens & Jeukendrup, 2003). 

21 



a) RAPID PHASE 

This phase occurs immediately following exercise and lasts between 30-

60 minutes (Jentjens & Jeukendrup, 2003; Price et al., 2000). This 

phase proceeds independently of insulin and it is suggested that it only 

occurs when muscle glycogen is depleted and carbohydrate is supplied 

immediately following exercise. The rate of muscle glycogen 

resynthesis during this phase is approximately 12-30 mmol/L/h (Price et 

al. , 2000). (Note that unfortunately it is not possible to compare values 

for muscle glycogen resynthesis across studies due to unit differences, as 

the writer did not provide enough information to allow conversion). 

A potential mechanism for this rapid phase is increased glycogen 

synthase activity immediately following exercise (Jentjens & 

Jeukendrup, 2003). Both muscular contraction and insulin have been 

shown to increase glycogen synthase activity. However, it now appears 

that muscle glycogen concentration is the more potent regulator of 

glycogen synthase activity, with an inverse relationship evident between 

muscle glycogen concentration and glucose transport stimulated by both 

insulin and muscular contraction (Jentjens & Jeukendrup, 2003). 

With this phase depending on the availability of carbohydrate to the 

muscle, it is important that immediately following exercise the athlete 

consumes some form of carbohydrate that can be quickly absorbed and 

readily available for incorporation into the replenishing muscle glycogen 

stores. 

22 



b) SLOWPHASE 

This phase of muscle glycogen synthesis occurs following the fast phase 

and requires the presence of both carbohydrate and elevated levels of 

insulin (Price et al, 2000; Jentjens & Jeukendrup, 2003). It is believed 

that this phase could last for several hours provided that carbohydrate 

supply is maintained, and is characterised by an increase in the cells' 

sensitivity to insulin, which in turn maintains ongoing glucose uptake 

and glycogen synthesis. The rate of muscle glycogen resynthesis during 

this phase has been observed at approximately 3 mmol/L/h (Price et al., 

2000). 

With this phase depending mainly on the presence of raised insulin 

levels, the athlete must consume some form of carbohydrate to elicit 

such a response, in addition to providing a steady supply of glucose for 

incorporation into the replenishing muscle glycogen stores. 

One way that the nutritional demands of both the fast and slow phases of 

muscle glycogen synthesis are met (i.e. a rapid supply of glucose and a high 

insulin response) is through the consumption of high glycaemic index 

carbohydrates. It is clearly evident that high muscle glycogen synthesis rates 

occur during the initial hours after exercise when a high glycaemic index 

carbohydrate is ingested (Jentjens & Jeukendrup, 2003). Consuming these high 

glycaemic index carbohydrates in liquid form, especially in the early period 

following cessation of exercise, may prove more effective than solid foods due 

to the faster gastric emptying and easier digestion of carbohydrate supplied in 

liquid form. The additional benefit of supplying carbohydrates in liquid form is 

that this will also aid in the athlete 's rehydration following exercise due to the 

osmotic effect of carbohydrates increasing water absorption. 

23 



In order to maximise the rate of glycogen resynthesis immediately following 

exercise, the timing of consumption of carbohydrate is very important. In a 

study by Ivy et al., (1988, cited in Levenhagen, et al, 2001) it was found that 

consumption of a 25% glucose polymer immediately following exercise 

dramatically increased the rate of glycogenesis. It was also found that the rate 

of glycogenesis was markedly decreased (by 45%) if ingestion of the glucose 

polymer was delayed by 2 hours. This finding is supported in a study by 

Levenhagen et al., (2001 ), where it was shown that peak stimulation of whole 

body glucose utilisation and leg glucose uptake occurred within the first hour 

after exercise. 

Research into the optimal amount of carbohydrate required to maximise muscle 

glycogen synthesis rates has produced conflicting results. In a recent review by 

Jentjens & Jeukendrup (2003) examining the amount of carbohydrate consumed 

and the resulting muscle glycogen synthesis rate (Figure 1.6), carbohydrate 

intakes of between 1.0-1.83 g/kg body weight (BWT)/h have led to very high 

glycogen synthesis rates when consumed at 15-60 minute intervals. From the 

literature it is reasonable to conclude that maximal glycogen synthesis rates 

occur at a carbohydrate intake of approximately 1.2 g/kg BWT/hour. In 

support of this conclusion, Van Loon et al., (2000b) demonstrated that 

increasing the carbohydrate intake during recovery from 0.8g/kg BWT/hour to 

1.2 g/kg BWT/hour resulted in a significantly greater plasma insulin response 

( 46 ±18%) and significantly higher muscle glycogen synthesis ( 44.8 ±6.8 µmol 

glycosol units/g dry muscle wt/h compared with 16.6 ±7.8 µmol glycosol 

units/g dry muscle wt/h). It should be noted, however, that in this study no 

difference was found between consumption of 1.2 g/kg BWT/hour of 

carbohydrate and consumption of a mixture of 0.8 g/kg BWT/hour of 

carbohydrate and 0.4 g/kg BWT/hour of protein. In this latter study by Van 

Loon et al., (2000b ), carbohydrate supplements were provided at 30-minute 

intervals. Studies that have supplemented at longer (2 hour) intervals may not 

find the same association between muscle glycogen synthesis rates with 

24 



increasing carbohydrate intake because they may not adequately increase and 

maintain blood glucose and insulin levels over the entire period (Jentjens & 

Jeukendrup, 2003). The choice of study design is important to ensure that study 

conditions closely mimic current post-exercise nutritional strategies used by 

athletes. The use of more frequent ingestion of carbohydrate is one way of 

achieving this and will therefore increase the applications of the research in 

terms of presenting practical recommendations. 

.$ 
50 

~ • (/) • "iii 40 •• <ll_ • • £ -E I • C: s: 
30 rn' 'U • • C: C) 

•• ). • • <l)~ • • 01-
0 0 20 u E 
2:-E 
01-

...9.1 10 • • &l 
::::, 
~ 

0 
0 0.5 1.5 2 

Carbohydrate intake (g/kg/h) 

Figure 1.6. Muscle glycogen synthesis rates are depicted against the rate of carbohydrate 
ingestion. The horizontal line depicts the absolute maximum for muscle glycogen synthesis 
(Jentjens & Jeukendrup, 2003). 

Carbohydrate intake following exercise may be of increased importance in 

cases where significant muscle damage has occurred during exercise. Muscle 

damage typically impairs the rate of post-exercise glycogen synthesis, 

especially following endurance exercise, where it has been proposed that this 

may be the result of decreased GLUT4 content in the muscle. However, in a 

study by Asp et al. (1997), it was found that following a marathon the GLUT4 

25 



content of muscle was unaltered. Further research on muscle damage and 

glucose uptake mechanisms by Aguila, et al. (2000) found that muscle damage 

impairs insulin stimulation of IRS-1, PI 3-kinase and Akt-kinase which leads to 

decreased insulin-mediated glucose uptake. These results indicate that it is the 

signalling of GLUT4 translocation into the cell membrane that causes impaired 

muscle glycogen synthesis as a result of muscle damage. This decreased rate of 

glucose uptake by the muscle may be partially overcome, however, by 

increased carbohydrate intake following exercise (Burke, 2000). Therefore, it 

is important for athletes to use nutritional strategies to maximise both the fast 

and slow phases of muscle glycogen synthesis. 

Protein is now also being included in exercise recovery beverages. It has been 

shown that the availability of amino acids to the muscle stimulates protein 

recovery (Tipton & Wolfe, 2001). Therefore, inclusion of protein in a recovery 

beverage may improve the athlete's recovery through the protein's synergistic 

effect on carbohydrate metabolism and a stimulatory effect on muscle recovery. 

1.3.3 . PROTEINS 

Protein is now being included as part of an athlete's recovery for two main 

reasons: firstly, protein seems to have a stimulatory effect on insulin levels, 

thus improving uptake of glucose into the glycogen depleted muscle, and 

secondly, dietary protein may also have an anabolic effect on muscle by 

providing the essential substrate amino acids needed to support muscle protein 

synthesis. 

26 



1.3.3.1.PROTEIN AND THE INSULIN RESPONSE 

The ingestion of protein, in addition to carbohydrate, following exercise has 

been suggested to accelerate muscle glycogen synthesis. The proposed 

mechanism is through an insulinotropic effect, eliciting an insulin response 

greater than that normally associated with ingestion of carbohydrate alone. 

There appears to be a link between insulin and protein metabolism which 

was highlighted in a study by Levenhagen et al., (2001) where the rate of 

protein synthesis was increased during the same period that insulin 

responsiveness to glucose metabolism appeared to be increased. Another 

suggested mechanism for protein enhancing muscle glycogen recovery is 

that following exercise protein may provide the carbon skeletons necessary 

to facilitate a gluconeogenic supply of glucose, thereby enhancing muscle 

glycogen synthesis (Zawadzki et al., 1992). 

A number of studies have shown the insulinotropic effect of protein to be 

very significant, with one study by Van Loon et al., (2000a), demonstrating 

an insulin response (from the intake of protein, in addition to carbohydrate) 

100% greater than that found from ingestion of carbohydrate alone. This 

increased insulin response may be a potential mechanism for promoting 

increased glycogen synthesis rates in the fatigued muscle. This was 

demonstrated in another study by Van Loon et al., (2000b) where glycogen 

synthesis rates were more than 113% higher than those found from the 

carbohydrate-only control group during a five hour post-exercise period. 

This finding also supported the earlier findings of Zawadzki et al., (1992) 

which described an increased rate of glycogen synthesis following 

consumption of protein, in addition to carbohydrate, during the exercise 

recovery period. The study by Zawadzki et al., ( 1992) showed that 

supplementation of protein alone was not enough to stimulate muscle 

glycogen synthesis, and that in this case the results did not differ from the 

response when no supplement was given. This finding aids in refuting the 

27 



argument that the higher glycogen synthesis rates observed when protein 

was consumed in addition to carbohydrate were the result of an increased 

gluconeogenic flux. Additionally, the higher concentration of insulin found 

in these studies would have acted to inhibit gluconeogenesis rather than 

stimulate it. The need for a recovery beverage containing carbohydrate and 

protein, as opposed to current I y available sports drinks ( containing 

carbohydrate only), was confirmed in a study by Williams et al., (2003). In 

this study it was found that a beverage containing carbohydrate and protein 

(supplying -0.8 g/kg of carbohydrate) resulted in a 17% greater plasma 

glucose response, a 92% greater insulin response and a 128% greater storage 

of muscle glycogen when compared with a 6% carbohydrate-electrolyte 

sports beverage (supplying ~.3g/kg carbohydrate). It is common practice 

for athletes to use sports drinks (actually designed for consumption during 

exercise) following exercise, whereas the use of a recovery beverage would 

appear to be more beneficial. 

Despite physiology providing logical support for the carbohydrate and 

protein mix in a post-exercise beverage, research on the effects of the co­

ingestion of carbohydrate and protein on muscle glycogen synthesis have 

produced conflicting results (Table 1.2). This is highlighted by differences 

in the methodology of these studies, in terms of the type of protein used, the 

inclusion of additional amino acids and the timing of beverage intake, which 

may influence the resultant muscle glycogen synthesis rates. Despite this, 

one strong theory emerged suggesting that the increase in muscle glycogen 

synthesis rates associated with protein intake, in combination with 

carbohydrate, may have been due to maximal glycogen synthesis rates not 

being reached with a moderate (~.8 g/kg/h) carbohydrate intake (Jentjens & 

Jeukendrup, 2003). One study, already mentioned, by Van Loon et al., 

(2000b) appeared to support this suggestion, when an increase in the rate of 

carbohydrate intake from 0.8 - 1.2 g/kg BWT/h resulted in higher muscle 

glycogen synthesis rates. 

28 



When the effects of this higher intake of carbohydrate (1.2 g/kg/h) was 

examined, however, it was found that the addition of a protein-amino acid 

mixture did not increase muscle glycogen synthesis rates, despite a much 

higher insulin response (Jentjens et al., 2001). This result supported the 

earlier research by Van Hall et al., (2000) which concluded that when 

carbohydrate was ingested in sufficient quantities, the co-ingestion of 

carbohydrate and protein provided no additional increase in glycogen 

resynthesis rates. These findings appeared to suggest that insulin is not the 

limiting factor for muscle glycogen synthesis when total carbohydrate intake 

is high ( 1.0-1.2 g/kg/h) and that the availability of carbohydrate post­

exercise plays a more important role (Van Loon et al. , 2000b). 

More recently, however, a study by Ivy et al., (2002) found that a 

carbohydrate and protein supplement resulted in higher muscle glycogen 

levels after four hours of exercise recovery compared with consumption of 

beverages containing either a high carbohydrate content (of equal energy 

value to the carbohydrate-protein beverage) or equal carbohydrate content 

without the protein. While no significant difference was found in the plasma 

insulin responses between treatments, the plasma glucose concentrations 

tended to be significantly lower in the carbohydrate-protein treatment. 

Although the amount of carbohydrate supplied in this study was low, it may 

suggest that protein has a role in the uptake of glucose into the muscle, 

above that seen from the consumption of carbohydrate alone. 

29 



Table 1.2. Summary of research examining the effect of the consumption of protein in addition to carbohydrate on insulin response and muscle glycogen 
resynthesis. 

Reference n Carbohydrate Protein Protein Types Used Time of Findings 
g/k~h ~k~h [ntake 

Zawadzki et 9 0.77 --- ---- 0, 120 • Plasma glucose concentration significantly higher for 
al., 1992. 0.77 0.28 Whey protein isolate Carb only trial compared to Carb + Protein trial. 

• Plasma insulin concentration significantly higher for 
Carb + Protein trial than Carb only trial. 

• Rate of muscle glycogen storage significantly faster in 
Carb + Protein trial compared to Carb only trial. 

Carrithers et 8 1.0 --- 0, 30, 60, 90, • No significant differences in muscle glycogen 
al., 2000 0.71 0.20 Whey protein/Casein mix 120,150, concentration, serum glucose or serum insulin between 

(included 0.09g/kg/h milk fat) 180,2 10 three trials. 
0.86 0.14 Essential amino acids 

Van Hall et 5 1.25 ---- ---- 0 (Bolus •No significant difference in muscle glycogen 
al., 2000a 1.25 0.38 Whey protein hydrolysate 600m), Then resynthesis rate. 

150ml/15mi • Arterial insulin levels significantly higher in the Carb + 
n for 4h Protein trial compared to the Carb only trial. 

Van Hall et 8 0.8 ---- ---- 0, 60, 120 • No significant difference in rate of muscle glycogen 
al., 2000b 0.8 0.3 Wheat protein hydrolysate resynthesis. Rates were higher after ingestion of whey 

0.8 0.3 Whey protein hydrolysate and wheat hydrolysate trials compared to control but not 
significant. 

• Plasma insulin concentration significantly higher 
following ingestion of the whey and wheat hydrolysate 
trials compared to the control. 

30 



Table 1.2. (continued)) 
Reference n Carbohydrate Protein Protein Types Used Time of Findings 

g/kg/h g/kg/h Intake 

Van Loon et 8 0.8 --- ---- 0,30,60,90 • Insulin responses positively correlated with plasma 
al., 2000a 0.8 0.4 Whey protein hydrolysate leucine, phenylalanine and tyrosine concentrations. 

0.8 0.4 Wheat protein hydrolysate •No significant difference between whey and wheat 
0.8 0.4 Pea protein hydrolysate protein hydrolysates on insulin concentration. 
0.8 0.4 Casein protein • Intact protein ingestion resulted in lower plasma amino 

(combinations of wheat acid levels and an insulin response that was not 
hydrolysate and/or free amino significantly different from the control. 
acids also included) • Carb + Wheat protein hydrolysate with added free 

leucine + phenylalanine resulted in highest insulin 
concentration. 

Van Loon et 8 0.8 ---- ---- 0, 30, 60, 90, • Plasma insulin levels and muscle glycogen synthesis 
al.,2000b 1.2 ---- ---- 120, 150, rates were significantly higher in Carb + Protein and 

0.8 0.4 Wheat hydrolysate 180,2 10, Carb ( l.2g/kg/h) trials than Carb (0.8g/kg/h) .. 
240,270 •No significant differences between Carb+Protein and 

Carb ( l .2g/kg/h) trials. 

Van Loon et 8 1.2 ---- ---- 0, 30, 60, 90, • Insulin responses positively correlated with plasma 
al., 2000c 1.2 0.2 Wheat protein hydrolysate 120, 150 leucine, phenylalanine and tyrosine concentrations. 

1.2 0.4 Wheat protein hydrolysate • Insulin response higher than Carb only and Carb + 
(combinations of wheat protein hydrolysate following ingestion of protein 
hydrolysate and free amino hydrolysate + added free leucine and phenylalanine 
acids also included) (0.4g/kg/h protein = higher insulin response than 

0.2g/kg/h) 

Jentjens et 8 1.2 ---- ---- 0, 30, 60, 90, • Plasma insulin: Significantly higher in Carb + Protein 
al., 2001 1.2 0.4 Wheat protein hydrolysate 120, 150 than Carb trial. 

• No significant differences for plasma g lucose or muscle 
glycogen synthesis. 

31 



Table 1.2. (continued)) 
Reference n Carbohydrate 

Ivy et al., 7 
2002 

~ 

0.54 
0.54 
0.73 

Protein 
~h 

0.19 

Protein Types Used 

not stated 

32 

Time of 
Intake 

0, 120 

Findings 

• Muscle glycogen significantly higher in Carb + Protein 
trial compared to other two trials. 

• No significant differences in plasma insulin levels. 
• Plasma glucose levels lower following Carb + Protein 

trial compared to other two trials. 



One possible explanation for the protein-carbohydrate synergistic effect may 

be that with muscle damage decreasing glucose absorption into muscle, the 

stimulatory effect of protein on muscle recovery following exercise may 

facilitate muscle cell repair and more specifically insulin-mediated glucose 

uptake mechanisms early during recovery, which will in tum promote 

greater glucose uptake and muscle glycogen synthesis. 

A number of different types of protein have been studied to determine 

whether their insulinotropic effects are similar. It has been found that the 

percentage of amino acids that stimulate secretion of insulin is the same for 

both whey and casein proteins (Fruhbeck, 1998). However, the higher 

proportion of branched chain amino acids in whey protein may lead to a 

greater synergistic effect with insulin on protein metabolism compared to 

casein protein. In a study by Van Loon et al., (2000a) the insulinotropic 

effects of protein hydrolysates (whey, wheat and pea) and intact protein 

( casein) were compared when provided in addition to carbohydrate m a 

recovery beverage, the composition of which is given in Table 1.3. The 

result for the intact protein (casein) was an insulin response that was not 

significantly different from that found with the control diet ( carbohydrate 

only) and tended to be less than the responses observed after ingestion of the 

whey and wheat protein hydrolysates. After ingestion of intact protein, 

plasma amino acid responses over the two hour period tended to be lower 

than that observed following ingestion of the protein hydrolysates. The 

conclusion from this study was that the use of protein hydrolysates (whey or 

wheat) was preferred to stimulate insulin secretion because this results in a 

more rapid increase in plasma amino acid levels during a two hour period 

following exercise compared to that occurring after ingestion of the intact 

protein. Another finding of this study by Van Loon et al., (2000a) was that 

insulin responses were positively correlated with plasma leucine, 

phenylalanine and tyrosine concentrations. Comparing the composition of 

the wheat and whey protein hydrolysates used in the study by Van Loon et 

33 



al. , (2000a) (Table 1.3) highlights that the whey protein consists of a higher 

percentage of leucine, while wheat protein contains a higher proportion of 

phenylalanine, with the tyrosine levels being similar. The resultant insulin 

response of these two proteins may be similar, should these protein 

compositions be reflected in the plasma following consumption. 

Table 1.3. Amino acid composition of hydrolysates of whey, pea and wheat protein, and 

intact casein protein (van Loon et al., 2000a). 

Amino acid Whe~ Pea Wheat Casein 
% by wt 

L-Alanine 4.7 3.8 1.8 3.1 
L-Cysteine 1.2 0.4 0.9 0.4 
L-Aspartate 5.4 4.4 0.2 3.7 
L-Glutamate 9.1 7.4 3.2 11.2 
L-Phenylalanine 2.4 3.2 4.8 5.4 
L-Glycine 1.6 2.8 2.8 1.9 
L-Histidine 1.6 1.7 1.6 3.2 
L-Isoleucine 5.1 2.4 2.6 5.8 
L-Lysine 8.4 5.9 8.3 
L-Leucine 8.7 5.1 5.6 JO.I 
L-Methionine 1.3 0.6 I. I 3.0 
L-Asparagine 4.4 3.8 1.9 3.7 
L-Proline 5.9 2.8 12.3 10.5 
L-Glutamine 7.4 6.6 29.0 11.2 
L-Arginine 2.0 6.9 2.2 3.8 
L-Serine 5.1 4.0 4.4 6.3 
L-Threonine 6.6 2.8 2.0 4.6 
L-Valine 4.5 2.7 3.0 7.4 
L-Tryptophan 1.2 1.4 
L-Tyrosine 2.3 2.6 2.5 5.8 

It should be noted that the role of protein in an athlete's recovery from 

exercise is not limited to the effects of insulin on restoration of carbohydrate 

stores depleted through exercise. Insulin has also been identified as an 

important factor in protein metabolism (Kimball et al., 2002). Acute 

34 



physiologic elevations in plasma insulin levels, especially during conditions 

of hyperaminoacidemia, result in an additional increase in net muscle 

protein anabolism in viva in humans (van Loon et al. , 2000c) . However, 

insulin should not be regarded as the primary regulator because in the 

absence of elevated amino acid concentrations, insulin only exerts a modest 

effect on muscle protein synthesis (van Loon et al., 2000c ). 

1.3.3.2.PROTEIN AND PROTEIN SYNTHESIS / DEGRADATION 

If an athlete can max1m1se protein synthesis and mm1m1se protein 

degradation in the first few hours following exercise then this would provide 

a situation promoting muscle remodelling and potentially hypertrophy. 

With protein degradation elevated during exercise, which continues into the 

post-exercise phase, protein intake following exercise is essential in the 

stimulation of muscle protein recovery. 

The metabolic basis for protein accretion from net muscle protein synthesis 

is a situation where protein synthesis exceeds protein breakdown over the 

given period in question (Tipton & Wolfe, 2004). It has been demonstrated 

that increased amino acid availability from exogenous amino acids elevates 

muscle protein synthesis and results in the maintenance of a positive net 

muscle protein balance following exercise (Tipton & Wolfe, 1998; Tipton & 

Wolfe, 2001). In the absence of food intake, the net response of protein 

metabolism to an acute bout of exercise remains negative (Rennie & Tipton, 

2000). Supplying amino acids during the early post-exercise period, at a 

time when blood flow to the muscle is increased, appears to promote greater 

amino acid availability and to maximise the stimulation of protein synthesis 

(Sawka et al., 2000). 

35 



The importance of amino acid availability on protein metabolism was also 

highlighted by Levenhagen et al., (2001) where the effect of providing a 

supplement ( containing a combination of protein ( casein), carbohydrate and 

lipid) either immediately following exercise (EARLY) or three hours post­

exercise (LA TE) was examined. Supplementation immediately following 

exercise resulted in an increased rate of protein synthesis compared with 

when the supplement was supplied three hours later. The rate of leg protein 

synthesis was three times greater for EARLY than that found for LA TE, 

while the whole body rate of protein synthesis was 12% greater with the 

supplement for EARLY compared with that found for LA TE (Figure 1. 7). 

There was no difference in the measurement for leg protein breakdown or 

whole body proteolysis between the two conditions (EARLY verses LATE). 

This study illustrates the importance of supplying amino acids immediately 

following exercise to stimulate protein recovery, with amino acid 

availability dictating the rate of protein synthesis during the recovery period. 

It also illustrates that protein synthesis is not only stimulated during the 

early stages 9f the recovery period, but protein synthesis also increased 

when protein was supplied three hours following exercise. Therefore, in 

order to maximise recovery following exercise, it is important to supply the 

athlete with protein during the early stages of recovery and to ensure a 

continued protein supply over at least the next three hours. This may 

potentially be achieved through the consumption of a combination of both 

protein hydrolysates and whole protein, because both these forms of protein 

would have varying rates of amino acid release during digestion. 

36 



] 

300 .. 

250 -

200 · 
e _-... 
[ ~ I.SO -

=-. 1111 • 100 .. 
&i "7 ...... s 
~ t 50 · 

5 ~ 0 

-SO , 

-100 -

(a) 

rJ 
8 2.5 

= S ~-...2.0 .. 

.9 '.s:: J 
.! ~ 1.5 I 
f: -:· 
c. ~1.0 I 
» bi) l J -!o.5 J 
j 
J 0.0 
~ 

-os I 
-1.0 

(b) 

• 

Protein Breakdown Protein Synthesis 

• 

Proteolysis Protein Synthesis 

•Ba.;;al 
•Early 
Ouite 

• 

Net Balance 

•Basal 
•Early 
Olate 

• 

Net Balance 

Figure 1.7. Rates of leg protein dynamics (a) and whole body protein dynamics (b) for 10 
subjects given an oral nutrient supplementation either immediately after exercise (EARLY) 
or 3 h postexercise (LATE). * Significantly different (p<0.05), EARLY vs LATE 
(Levenhagen et al., 2001). 

Hyperaminoacidemia has been shown to enhance the rate of muscle protein 

synthesis both at rest and following exercise (Rennie & Tipton, 2000). 

However, in a study by Biolo et al., (1997) it was found that infusion of an 

amino acid mixture after exercise enhanced the rate of muscle protein 

synthesis compared with the infusion of mixed amino acids at rest. This 

37 



finding, also supported in recent research by Tipton et al., (2003), suggests 

an additive effect between the availability of amino acids and the effects of 

exercise on the muscle and that this early post-exercise effect (in response to 

consumption of essential amino acids) reflects the 24-hour post-exercise 

response. The study by Biolo et al. , ( 1997) also showed that during the 

period of hyperaminoacidemia after exercise the rate of muscle protein 

breakdown, which is normally elevated, did not rise. While this study 

examined the effect of the intravenous infusion of amino acids, it has also 

been shown that oral amino acid ingestion is effective in ensuring amino 

acid availability to the muscle following exercise (Rennie & Tipton, 2000). 

In a further study by Biolo et al. , (1999) the normal post-exercise 

stimulation of protein breakdown was ameliorated by local insulin infusion 

after exercise. Therefore, consumption of amino acids in addition to 

carbohydrates (insulin release stimulatory) may promote an optimal protein 

balance in the muscle following exercise. 

The ability of dietary protein to have an effect on protein synthesis and 

degradation was highlighted in a study by Boirie et al., (1997), which 

examined the effects of whey and casein on amino acid absorption and the 

resulting effects on protein metabolism. When subjects were given whey 

protein, it was found that the plasma appearance of dietary amino acids was 

fast, elevated and transient, a profile that was associated with an increase in 

protein synthesis with no change in protein degradation. When athletes 

were given the casein protein, it was found that the plasma appearance of 

dietary amino acids was slower, less elevated and more prolonged compared 

to that seen for the whey protein. This pattern was associated with a slight 

increase in protein synthesis, and a marked decrease in protein degradation. 

In this study by Boirie et al., (1997) it was proposed that the differences 

were mainly the result of differences in the gastric emptying of these two 

proteins. This proposed difference in the gastric emptying, and therefore 

supply of amino acids, from different proteins, has lead to more focus on the 

38 



use of whey protein, often in the form of protein hydrolysates, as opposed to 

intact protein, as the preferred form of dietary protein for exercise recovery. 

As protein hydrolysates contain smaller amino acid chains ( depending on 

the degree of hydrolysis), the absorption of amino acids from the protein 

may be faster as less digestion is required compared to the release of amino 

acids from intact protein. However, the effect of whole protein or 

hydrolysates of whole protein on protein synthesis and degradation remains 

unclear. 

In nutrition research related to exercise recovery, the protein hydrolysates 

used are mainly derived from two major sources: whey protein and wheat 

protein. With whey protein containing the higher proportion of branched 

chain amino acids, the milk protein may have an advantage over wheat 

protein. Table 1.4 highlights the leucine and other branched chain amino 

acid contents of different proteins. While the availability of amino acids is a 

limiting factor for protein synthesis, it appears that the branched chain 

amino acid leucine, in particular, is involved in stimulating protein synthesis 

(Kimball et al., 2002; Layman & Baum, 2004). The regulatory role of 

leucine on protein synthesis appears to depend on its intracellular 

concentration, and it is now known to involve regulation of the insulin 

signalling pathway. The site of leucine action is on the kinase mTOR 

(mammalian target of rapamycin) (Figure 1.8), which acts to stimulate rates 

of protein synthesis via two pathways: phosphorylation control of eIF4 

translational initiating complex and from activation of S6 ribosomal protein 

(Layman & Baum, 2004). Parallel to the effects on protein synthesis, 

mTOR has been shown to potentially alter the insulin receptor signal via a 

stimulation of upstream phosphorylation of IRS-1 (insulin receptor 

substrate) (Layman & Baum, 2004). At rest, this down-regulation of the 

insulin signal did not affect glucose transport, potentially due to either ( 1) 

basal levels of GLUT4 transporters being adequate to maintain glucose 

transport or (2) that levels of GLUTl (non-insulin dependent glucose 

39 

,, 



transporters) may play an important role maintaining baseline levels of 

glucose transport (Layman & Baum, 2004). It is unknown wha