The physiological effects of pseudoephedrine on endurance cycling : a thesis submitted in the partial fulfilment of the requirements for the degree of Master of Science in Sport and Exercise Science, Massey University (Palmerston North, New Zealand)
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Date
2008
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Massey University
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Abstract
Background: Pseudoephedrine (PSE) is a mild central nervous system stimulant
that when consumed at a high dosage has the potential to alter physiological and
psychophysical responses. PSE is widely accessible as over-the-counter
medication and despite limited research into PSE at high dosages or its effects on
prolonged exercise (>2 hours) is no-longer on the World Anti-Doping Association’s
banned substance list. Currently unrestricted in sport and with no real
understanding of the abovementioned responses during endurance exercise there
is a high potential for abuse in sport. A recent study performed in our laboratory
found PSE to improve self-paced cycling performance in some individuals,
however no physiological measurements were taken
Purpose: The primary purpose of this study was to determine the physiological
effects of PSE at a dosage previously shown to improve performance (2.5 mg/kg)
in some individuals during prolonged cycling. A secondary purpose of this study
was to assess the effect on endurance cycling performance.
Methods: In a randomized, double-blind and counter-balanced design, ten welltrained
cyclists participated in two trials, consisting of 120 min of fixed-intensity
cycling at 65% VO2max followed by a set work, self-paced time-trial (TT) of ~30 min,
following ingestion of either 2.5 mg/kg PSE or visual-matched glucose placebo.
Venous blood samples were collected before and during exercise, along with body
temperatures and heart rate. Perceived effort and expired gas samples were
collected during exercise. Exercise and diet was controlled ~48-hours prior to the
trials.
Results: Mean heart rate was significantly higher with PSE (P = 0.028) during
fixed-intensity exercise. Blood glucose concentrations were significantly lower with
PSE (P <0.001) for the first 40 min of fixed-intensity exercise. Respiratory
exchange ratio was lower in the final 20-min of fixed-intensity and TT with PSE. Blood lactate, perceived effort, ventilation, and body temperatures were not
significantly different between conditions during exercise, nor was TT performance;
however individual response was variable.
Conclusions: PSE ingestion increased heart rate during endurance cycling and
initially suppressed carbohydrate release into the bloodstream while increasing fat
oxidation in the later stages of exercise. Despite individual responses, endurance
cycling performance remained unchanged with PSE ingestion.
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Keywords
Cycling performance, Physiological measurements