Electrical Stimulation-induced Fatigue In The Contralateral Leg Impairs Endurance Exercise Performance

Abstract

During fatiguing exercise, the development of peripheral fatigue and the associated increased firing of group III/IV afferent fibres, promote central fatigue. PURPOSE: The aim of this study was to assess whether peripheral fatigue in the contralateral leg induced by electrical quadriceps stimulation to bypass central command, would impair endurance performance of the subsequently exercising ipsilateral leg. METHODS: Eight young healthy males were recruited for this study. After completing an incremental test to exhaustion on a single-leg knee extensor ergometer, the subjects performed two tests on separate days. On the first day, they performed a time-to-exhaustion test at 85% of their maximal power output (No-PreF trial). Exercise-induced quadriceps muscle fatigue was assessed by supramaximal electrical femoral nerve stimulation evaluating changes in the potentiated resting twitch force (Qtw,pot), maximal voluntary contraction (MVC) and voluntary activation (VA) from pre to post exercise. On the second day, the same exercise bout was preceded by the induction of fatigue in the contralateral quadriceps through electrical stimulation (PreF trial). The pre-fatiguing protocol was terminated once the subjects reached the maximum tolerance score on a 1-10 visual analogue scale (duration: 6.6 ± 0.9 min). Integrated electromyography (iEMG) was recorded and used to estimate spinal motoneuronal output. RESULTS: Time to exhaustion in the PreF trial was reduced by 41% (9.1 ± 1.5 to 5.4 ± 1.2 min, p < 0.05). The reduction in MVC (-36 ± 8 vs -23 ± 10%, p < 0.05) and Qtw,pot (-53 ± 3 to -39 ± 9% p < 0.05) was more accentuated in the No-PreF trial compared to PreF. Conversely, VA was more affected in PreF than in No-PreF (-20 ± 7 vs -14 ± 5%, p < 0.05). At every submaximal time point, iEMG was significantly higher in PreF compared to No-PreF, while at exhaustion it was higher in the latter (p<0.05). CONCLUSIONS: Pre-induced muscle fatigue in the contralateral limb impairs endurance performance of the exercising ipsilateral limb. This cross-over effect of fatigue is likely mediated by the inhibitory influence associated with group III/IV muscle afferent feedback and not related to changes associated with central command.Funding: No funding was received for this study