Effect of prior exercise at different pedalling frequencies on maximal power in humans

Summary

The effect of prior submaximal exercise performed at two different pedalling frequencies, 60 and 120 rev · min⁻¹, on maximal short-term power output (STPO) was investigated in seven male subjects during cycling exercise on an isokinetic cycle ergometer. Exercise of 6-min duration at a power output equivalent to 92 (SD 5)% maximal oxygen uptake$\left( {\dot VO_{2max} } \right)$, whether performed at a pedalling frequency of 60 or 120 rev · min⁻¹, reduced maximal STPO generated at 120 rev · min⁻¹ to a much greater extent than maximal STPO at 60 rev · min⁻¹. After 6-min submaximal exercise at 60 rev · min⁻¹ mean reductions in maximal STPO measured at 120 and 60 rev · min⁻¹ were 27 (SD 11)% and 15 (SD 9)% respectively, and were not significantly different from the reductions after exercise at 120 rev · min⁻¹, 20 (SD 13)% and 5 (SD 9)%, respectively. In addition, we measured the effect of prior exercise performed at the same absolute external mechanical power output [236 (SD 30)W] with pedalling frequencies of 60 and 120 rev · min⁻¹, Although the external power output was the same, the leg forces required (absolute as well as expressed as a proportion of the maximal leg force available at the same velocity) were much higher in prior exercise performed at 60 rev · min⁻¹. Nevertheless, maximal STPO generated at 120 rev · min⁻¹ was reduced after exercise at 120 rev-min⁻¹ [20 (SD 13) %,P<0.05] whereas no significant reduction in maximal STPO was found after prior exercise at 60 rev · min⁻¹. The present findings would suggest that exercise performed at 92 (SD 5)%$\dot VO_{2max}$, whether at 60 or at 120 rev · min⁻¹, selectively fatigues the faster fatigue-sensitive fibres resulting in a greater reduction in maximal STPO generated at 120 compared to 60 rev · min⁻¹. The greater fatigue of maximal STPO generated at 120 rev · min⁻¹ due to exercise performed at a power output of 236 (SD 30)W at 120 rev · min⁻¹ compared to 60 rev · min⁻¹ would suggest a relatively greater contribution of fast fatigue-sensitive fibres when higher movement frequencies and hence different muscle shortening velocities are used at this submaximal exercise intensity.