## 7 Discussion
The maximal power output by a muscle can only be generated when it is moving at its own specific optimal velocity [8; 29]. Although, practically, in connection with locomotion, velocity can only be determined globally for all the muscles involved, the importance of specific individual optimal velocities is unquestionable [21]. A variety of studies have demonstrated that maximal mechanical performance during cycling can only be achieved at the individual optimal cadence (e.g., [5; 6; 11; 12; 29; 30; 31]). In the case of maximally activated muscles, all fiber types (I, IIa, IIx) are expected to contribute to power output, so long as they are not completely fatigued and their maximal velocity of shortening is not exceeded [21]. The effect of fatigue on dynamic muscle function as expressed in the F/v and P/v profiles has rarely been investigated. [PERSON], [PERSON], and their colleagues [17; 18] reported that, with increasing fatigue, the F/v profile shifts in a parallel mode towards the origin, which corresponds to a linear decrease in velocity at constant resistance. A number of findings indicate that the parallel shift in the initially fatigue-free profile in maximal sprints is caused by an approximately simultaneous decrease in force development and in the contraction velocity of high-glycolytic fast-twitching muscle fibers, resulting in a decline in the number of active muscle fibers as they become fully fatigued [4; 32; 33; 34]. If this is the case, the time course of the optimal cadence may reflect the time course of the recruitment of different types of muscle fibers as well as their metabolic state. As fatigue increases, the optimal cadence should approach the rate that can be sustained by all fibers with sufficient endurance to continue being activated (i.e., I and IIa). If the effort is prolonged, successive fatigue in IIa fibers will likely cause a further drop in the profile. Assuming systematic changes in the force-velocity profile due to fatigue-related elimination of predominantly phosphatic and glycolytic fast-twitching muscle fibers during the first 60 s of all-out exercise, the combined optimal cadence of the fibers with sufficient endurance can be defined as the limiting value for the function modelling the optimal dynamic cadence (5). Here, c = PRoptkRlla describes the common optimal cadence of type I and IIa fibers, reflecting the optimal power generation for endurance events lasting only a few minutes. Based on our results, the cadence resulting in the greatest power output during maximal endurance exercise with maximal oxygen uptake appears to be approximately 62 rpm. This agrees with a number of other reports [29; 35; 36; 37; 38] that the cadence that generates power most efficiently during low- to moderate-intensity exercise is in the range of 42-71 rpm. In endurance racing, professional cyclists prefer a cadence close to 90 rpm [6]. We assume that this is because during their regular training, they pedal at such rates, which results in improved motor coordination and reduced neuromuscular fatigue under these conditions [38]. Moreover, competing with the same cadence employed during training probably lowers the accumulation of metabolites during races lasting for several hours, due to shorter contractions and less restriction of blood flow [4]. Our findings reveal that the mean power during the sprint depends strongly on the fatigue-free maximal power and maximal force, as well as on the time constant in the function describing the time-dependent changes in optimal pedaling rate. Pmax and Fmax characterize an athlete's fatigue-free level of performance, whereas \(\tau\) represents his/her resistance to fatigue. With respect to the calculated linear influence of these parameters on Pmean, the fatigue-free level of power appears to exert a greater impact than the time constant of the loss of power induced by fatigue.