Original articles

Exercising with reserve: evidence that the central nervous system regulates prolonged exercise performance

J Swart¹, R P Lamberts¹, M I Lambert¹, A St Clair Gibson², E V Lambert¹, J Skowno³, T D Noakes¹

¹ UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Sports Science Institute of South Africa, Newlands, South Africa
² School of Psychology and Sports Sciences, Sports Sciences, Northumbria University, Newcastle upon Tyne, UK
³ Department of Anaesthesia, University of Cape Town, Cape Town, South Africa

^{Correspondence to} Dr J Swart, UCT/MRC Research Unit for Exercise Science and Sports Medicine, Sports Science Institute of South Africa, PO Box 115, Newlands 7725, South Africa; jeroen.swart{at}uct.ac.za

Objective: The purpose of this study was to measure the effects of an amphetamine (methylphenidate) on exercise performance at a fixed rating of perceived exertion of 16.

Methods: Eight elite cyclists ingested 10 mg methylphenidate in a randomised, placebo-controlled crossover trial.

Results: Compared with placebo, subjects receiving methylphenidate cycled for approximately 32% longer before power output fell to 70% of the starting value. At the equivalent time at which the placebo trial terminated, subjects receiving methylphenidate had significantly higher power outputs, oxygen consumptions, heart rates, ventilatory volumes and blood lactate concentrations although electromyographic activity remained unchanged. The ingestion of a centrally acting stimulant thus allowed subjects to exercise for longer at higher cardiorespiratory and metabolic stress indicating the presence of a muscular reserve in the natural state.

Conclusions: This suggests that endurance performance is not only "limited" by mechanical failure of the exercising muscles ("peripheral fatigue"). Rather performance during prolonged endurance exercise under normal conditions is highly regulated by the central nervous system to ensure that whole-body homeostasis is protected and an emergency reserve is always present.

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