Investigating the bioenergetic and mathematical determinants of the Critical Power model in elite cyclists : a thesis presented in partial fulfilment of the requirements for the degree of Master of Health Science in Sport and Exercise at Massey University, Manawatū, New Zealand

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Background: The Critical Power model is used to monitor and predict the performance of elite cyclists. Using maximal power data from various durations the model calculates a maximal steady state intensity called Critical Power and a work capacity beyond this known as the W' (W-Prime). Much research has focussed on the bioenergetics of the Critical Power, however, less is known about the bioenergetic composition of the W'. Aim: The key aim of this study was to investigate the bioenergetics of the Critical Power model. Secondary aims were to compare four different Critical Power models against each other and determine the relationship between V̇Lamax and power output during extreme intensity exercise. Hypothesis: It was hypothesised that measures related to anaerobic pathways (Peak power, V̇Lamax) would better predict W', while measures related to aerobic pathways (Wmax, V̇O2max, VT1 and VT2 power outputs) would better predict CP. Methodology: Ten elite national level male cyclists participated in the study, with nine completing the study. Participants reported to the laboratory on three occasions separated by at least 24h, over a period of less than three weeks. In the first session participants completed a test to determine V̇Lamax, a 1-min time trial (TT), and a ramp test to determine V̇O2max, Wmax, VT1, and VT2. In the subsequent two sessions participants completed maximal four and ten-minute TT's which were used to determine Critical Power and W' using the Linear Time-Work model for the primary analysis. In the secondary analysis four Critical power models were formulated from all three TT efforts and compared against each other, while the 1-min TT was used to assess extreme intensity exercise capability. Results: CP was strongly correlated with the aerobic variables VT1 (r=0.72, r2=0.52, p=0.028), VT2 (r=0.85, r2=0.73, p=0.0035), V̇O2max (r=0.91, r2=0.83, p=0.0007) and Wmax (r=0.92, r2=0.84, p=0.0005). Power outputs at CP and VT2 were not significantly different for absolute (327 ± 41 vs 330 ± 37W, p=0.91) or relative (4.66 ± 0.54 vs 4.72 ± 0.58W·kg-1, p=0.95) power output. The only significant relationships with W' were with V̇O2max (ml·min-1·kg-1)(r=-0.67, r2=0.45, p=0.047) and CP (W·kg-1) (r=-0.69, r 2=0.47, p=0.042). Using variables related to bioenergetics multiple regression significantly predicted CP(W·kg-1) (p=0.001) and W (p=0.034). The relative power output (W·kg-1) in the 1-min TT was significantly related to V̇Lamax (r=0.85, r2=0.73, p=0.0016), although work completed above CP in this effort was significantly less than W' (p=0.0008). All four Critical Power models were found to produce significantly different (p<.001) Critical Power and W' values, however, Critical Power was not significantly different to VT2 for any model (p=0.10-0.93). V̇Lamax could be significantly predicted from regression equations using both absolute (p=0.011) and relative (p=0.004) lactic interval power. Conclusion: The Critical Power is further reinforced as an aerobic parameter, while W' categorisation is more difficult due to the involvement of maximal aerobic capability and both anaerobic systems. W' was negatively correlated with measures of relative aerobic capability (V̇O2max ml·min-1·kg-1, CP W·kg-1) and has been related positively to lean mass in previous research, indicating a possible link between muscle mass and W'. The relationship between V̇Lamax and relative 1-min TT power output (W·kg-1) supported the extreme intensity exercise domain being highly related to glycolytic capacity. The fact W' could not be depleted in this effort was hypothesised to occur due to a delay in the V̇O2 kinetics and therefore a delayed contribution of the Critical Power to the effort. All models produced significantly different outputs for Critical Power and W'. Although the Critical power was not significantly different to VT2 for any model, the individual variation in Critical Power between models and lack of criterion measure with which to validate an accurate W' makes it difficult to recommend a best model. Finally, the V̇Lamax was significantly predicted by power over the lactic power interval of the V̇Lamax test which may be useful for those wishing to measure the V̇Lamax of elite cyclists without specialist equipment.