Nd the physical profiles of top-class male and female Kenyan long-distance runners. Method The subjects were 20 elite Kenyan runners: 13 men (10-km performance time: 10-km performance time of 28 min, 36 s ± 18 s) and 7 women (32 min, 32 s ± 65 s). The male runners were separated into high-speed training runners (HST:N = 6) and low-speed training runners (LST:N = 7) depending on whether they train at speeds equal or higher than those associated with the maximal oxygen uptake (vV̇O2max). All but one woman were high-speed training runners (female HST:N = 6). Subjects performed an incremental test on a 400-m track to determine V̇O2max, vV̇O2max, and the velocity at the lactate threshold (vLT). Results Within each gender among the HST group, 10-km performance time was inversely correlated with vV̇O2max (rho = −0.86, P = 0.05, and rho = −0.95, P = 0.03, for men and women, respectively). HST male runners had a higher V̇O2max, a lower (but not significantly) fraction of vV̇O2max (FV̇O2max) at the lactate threshold, and a higher energy cost of running (ECR). Among men, the weekly training distance at vV̇O2max explained 59% of the variance of vV̇O2max, and vV̇O2max explained 52% of the variance of 10-km performance time. Kenyan women had a high V̇O2max and FV̇O2max at vLT that was lower than their male HST counterparts. ECR was not significantly different between genders. Conclusion The velocity at the V̇O2max is the main factor predicting the variance of the 10-km performance both in men and women, and high-intensity training contributes to this higher V̇O2max among men....

Myostatin (Mstn) participates in the regulation of skeletal muscle size and has emerged as a regulator of muscle metabolism. Here, we hypothesized that lack of myostatin profoundly depresses oxidative phosphorylation-dependent muscle function. Toward this end, we explored Mstn ^−/− mice as a model for the constitutive absence of myostatin and AAV-mediated overexpression of myostatin propeptide as a model of myostatin blockade in adult wild-type mice. We show that muscles from Mstn ^−/− mice, although larger and stronger, fatigue extremely rapidly. Myostatin deficiency shifts muscle from aerobic toward anaerobic energy metabolism, as evidenced by decreased mitochondrial respiration, reduced expression of PPAR transcriptional regulators, increased enolase activity, and exercise-induced lactic acidosis. As a consequence, constitutively reduced myostatin signaling diminishes exercise capacity, while the hypermuscular state of Mstn^−/− mice increases oxygen consumption and the energy cost of running. We wondered whether these results are the mere consequence of the congenital fiber-type switch toward a glycolytic phenotype of constitutive Mstn ^−/− mice. Hence, we overexpressed myostatin propeptide in adult mice, which did not affect fiber-type distribution, while nonetheless causing increased muscle fatigability, diminished exercise capacity, and decreased Pparb/d and Pgc1a expression. In conclusion, our results suggest that myostatin endows skeletal muscle with high oxidative capacity and low fatigability, thus regulating the delicate balance between muscle mass, muscle force, energy metabolism, and endurance capacity.

This study examined the hypothesis that running speed over 800- and 1,500-m races is regulated by the prevailing anaerobic (oxygen independent) store (ANS) at each instant of the race up until the all-out phase of the race over the last several meters. Therefore, we hypothesized that the anaerobic power that allows running above the speed at maximal oxygen uptake (V̇o_2max) is regulated by ANS, and as a consequence the time limit at the anaerobic power (tlim PAN = ANS/PAN) is constant until the final sprint. Eight 800-m and seven 1,500-m male runners performed an incremental test to measure V̇o_2maxand the minimal velocity associated with the attainment of V̇o_2max( vV̇o_2max), referred to as maximal aerobic power, and ran the 800-m or 1,500-m race with the intent of achieving the lowest time possible. Anaerobic power (PAN) was measured as the difference between total power and aerobic power, and instantaneous ANS as the difference between end-race and instantaneous accumulated oxygen deficits. In 800 m and 1,500 m, tlim PAN was constant during the first 70% of race time in both races. Furthermore, the 1,500-m performance was significantly correlated with tlim PAN during this period ( r = −0.92, P < 0.01), but the 800-m performance was not ( r = −0.05, P = 0.89), although it was correlated with the end-race oxygen deficit ( r = −0.70, P = 0.05). In conclusion, this study shows that in middle-distance races over both 800 m and 1,500 m, the speed variations during the first 70% of the race time serve to maintain constant the time to exhaustion at the instantaneous anaerobic power. This observation is consistent with the hypothesis that at any instant running speed is controlled by the ANS remaining.

The purpose of the present investigation was 1) to study the effects of fitness level on perceived exertion (RPE) and estimated time limit (ETL) scales during exhausting runs, and 2) to predict time to exhaustion from RPE or ETL values collected during a constant run exercise. Eight high-fitness level and twelve moderate-fitness level endurance trained males performed two exhausting exercises on a 400-m running track. The first test was a graded exercise using a portable metabolic system to determine maximal oxygen uptake (V·O₂max), the velocity associated with V·O₂max (vV·O₂max), the velocity at the lactate threshold (vLT) and the velocity at delta 50 (vΔ50 : the velocity halfway between vV·O₂max and vLT). The second test was a constant run exercise at vΔ50 to determine the time to exhaustion at this intensity (tlimvΔ50). Moderate-fitness level athletes perceived exercise to be relatively more strenuous and felt that they could continue for less time than high-fitness level athletes at similar relative velocities. There was no effect of fitness level on perceived exertion for a given relative exercise duration. RPE corresponding to vLT was not statistically significantly different between the two levels groups. For the two groups, measured and predicted exhaustion time values, which were calculated from linear extrapolation of RPE and ETL values collected during the first 4 minutes of a submaximal constant run exercise, were not statistically significantly correlated. These results indicate that the aerobic fitness level seems to influence perceived exertion only during graded exercise. Consequently, if RPE is used to prescribe an exercise intensity, the prescription must be individualised regarding the aerobic fitness level of the athlete except for exercise intensities corresponding to vLT. Moreover, the perceived exertion pattern at the beginning of a submaximal constant run exercise could not be considered as a sensitive predictor of the point of self-imposed exhaustion whatever the fitness level of the athletes.