Human Muscle Fibre Types and Mechanical Efficiency During Cycling
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In prolonged high intensity exercise it seems advantageous in terms of resisting fatigue to choose relatively fast pedalling rates of ~100 rev/min. This advantage may be due to the greater reserve of power generating capacity at the higher pedalling rates, that is the difference between the power output required for the prolonged exercise and the maximum peak power measured at the same velocity. This is because the maximum power/velocity relationship in cycling exercise has been shown to be parabolic in form with an optimum velocity (Vopt) for maximum power occurring at a pedalling rate of around 120 rev/min (for discussion see ref. 9). The theoretical advantage of choosing fast pedalling rates for sustained high intensity exercise would however be negated if there was a disproportionate increase in the energy cost for the same external power output, that is if the mechanical efficiency decreased. Before considering this issue, however, it is interesting to see what trained cyclists actually do. We therefore asked a group of fit competitive cyclists to cycle around a very large flat indoor arena on their own bicycles at constant speed. Each cyclist performed a series of trials at constant speeds ranging from 20 to 47 km/hr. They were allowed to choose their own gear ratios. The data in Figure 1 shows that as the exercise intensity increased, expressed here as oxygen uptake (̇VO2), so did the freely chosen pedalling rate, an observation that is in agreement with previous reports (3, 5,7).
KeywordsMechanical Efficiency High Intensity Exercise Velocity Relationship Pedalling Rate Fibre Population
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