Introduction: Females have been shown to experience less neuromuscular fatigue than males in knee extensors (KE) and less peripheral fatigue in plantar flexors (PF) following ultra-trail running, but it is unknown if these differences exist for shorter trail running races and whether this may impact running economy. The purpose of this study was to characterize sex differences in fatigability over a range of running distances and to examine possible differences in the postrace alteration of the cost of running (Cr).Methods: Eighteen pairs of males and females were matched by performance after completing different races ranging from 40 to 171 km, divided into SHORT vs LONG races (< 60 and > 100 km, respectively). NM function and Cr were tested before and after each race. NM function was evaluated on both KE and PF with voluntary and evoked contractions using electrical nerve (KE and PF) and transcranial magnetic (KE) stimulation. Oxygen uptake, respiratory exchange ratio and ventilation were measured on a treadmill and used to calculate Cr.Results: Compared to males, females displayed a smaller decrease in maximal strength in KE (−36% vs −27%, respectively, p < 0.01), independent of race distance. In SHORT only, females displayed less peripheral fatigue in PF compared to males (Δ peak twitch: −10% vs −24%, respectively, p < 0.05). Cr increased similarly in males and females.Conclusion: Females experience less neuromuscular fatigue than men following both 'classic' and 'extreme' prolonged running exercises but this does not impact the degradation of the energy cost of running.

No abstract

No abstract

Cervicomedullary stimulation provides a means of assessing motoneuron excitability. Previous studies demonstrated that during low-intensity sustained contractions, small cervicomedullary evoked potentials (CMEPs) conditioned using transcranial magnetic stimulation (TMS-CMEPs) are reduced, whilst large TMS-CMEPs are less affected. Since small TMS-CMEPs recruit motoneurons most active during low-intensity contractions while large TMS-CMEPs recruit a high proportion of motoneurons inactive during the task, these results suggest that reductions in motoneuron excitability could be dependent on repetitive activation. To further test this hypothesis, this study assessed changes in small and large TMS-CMEPs across low- and high-intensity contractions. Twelve participants performed a sustained isometric contraction of the elbow flexor for 4.5 min at the electromyography (EMG) level associated with 20% maximal voluntary contraction force (MVC; low-intensity) and 70% MVC (high-intensity). Small and large TMS-CMEPs with amplitudes of ~15 and ~50% Mmax at baseline, respectively, were delivered every minute throughout the tasks. Recovery measures were taken at 1, 2.5 and 4-min post-exercise. During the low-intensity trial, small TMS-CMEPs were reduced at 2-4 min (p≤0.049) by up to −10% Mmax, while large TMS-CMEPs remained unchanged (p≥0.16). During the high-intensity trial, small and large TMS-CMEPs were reduced at all time-points (p<0.01) by up to −14% and −33% Mmax, respectively, and remained below baseline during all recovery measures (p≤0.02). TMS-CMEPs were unchanged relative to baseline during recovery following the low-intensity trial (p≥0.24). These results provide novel insight into motoneuron excitability during and following sustained contractions at different intensities, and suggest that contraction-induced reductions in motoneuron excitability depend on repetitive activation.