[Frontiers in Bioscience E2, 779-792, January 1, 2010]

CNS fatigue provoked by prolonged exercise in the heat

Lars Nybo

Section of Human Physiology, Department of Exercise and Sport Sciences, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen O, Denmark

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. The evidence for CNS fatigue
3.1. Dynamic exercise
4. CNS factors influencing fatigue
4.1. Influence from pharmacological or nutritional interventions
4.2. Serotonergic activity
4.3. Dopamine and Noradrenalin
4.4. Caffeine
5. Summary and perspectives
6. Acknowledgement
7. References

1. ABSTRACT

Exercise-induced hyperthermia is associated with central fatigue as indicated by an impaired ability to sustain maximal motor activation during prolonged voluntary efforts. Therefore, exercise in hot environments challenges not only to the cardiorespiratory and locomotive systems but also to the brain. However, exercise with superimposed hyperthermia is not only a challenge to the brain it also provides an excellent model for studying factors of importance for central fatigue. Excessive heat storage within the brain appears to be the primary cause for the central fatigue during exercise in the heat, but pharmacological manipulations provide evidence for involvement of the dopaminergic system and other monoamines. Thus, enhanced dopaminergic activity may counteract hyperthermia mediated central fatigue and improve performance in the heat, while noradrenaline re-uptake inhibition appears to aggravate central fatigue and degrade exercise performance. Hyperthermia mediated central fatigue may include other cerebral perturbations such as reduced perfusion of the brain, accumulation of ammonia or depletion of neuronal energy stores, but further research is needed to elucidate their possible contributions.