Holistic approaches to understanding mechanisms of fatigue in high-intensity sport

Abstract

Purpose: The purpose of this article is to provide a holistic understanding of likely mechanisms of fatigue during high-intensity sports lasting 1–10 min. Methods: The contributions from skeletal muscle, central nervous system (motor drive), and fatigue sensations to lower performance during intense cycling, running, rowing, repeated sprints, or knee extensions were evaluated. Results: At the end of exercise, reductions of external power, force, or velocity and peak isometric forces are moderate (10–30%), motor drive falls by <8%, and fatigue sensations are extreme, e.g., Borg's rating of perceived exertion >18. Multiple putative fatigue factors can change simultaneously to interactively lower performance and/or provide protection. Major detrimental factors include raised intramuscular inorganic phosphate, severe extra- and intracellular acidosis, cerebral hypoxemia, large reduction of trans-sarcolemmal K⁺-gradient (also Na⁺- and Cl⁻-gradients), and reduced muscle glycogen levels. Factors resisting fatigue include elevated adrenaline, extracellular lactate, interstitial [H⁺] and [K⁺], and a normal trans-sarcolemmal Cl⁻-gradient. Conclusions: Raised inorganic phosphate interacting with intracellular H⁺, and a large rundown of trans-sarcolemmal ion gradients are likely to cause peripheral fatigue. Severe arterial hypoxemia (due to plasma acidosis, raised core temperature, lowered P_aO₂), and factors released from glycogen lowered muscles, e.g., interleukin-6, may cause central fatigue and strong fatigue sensations.

Keywords:

• muscle fatigue
• voluntary activation
• exhaustion
• acidosis
• potassium
• hypoxemia

Acknowledgements

The author gratefully thanks Sarah-Kate Miller and Dr Phil Weiser for comments on the manuscript.

Notes on contributor

Simeon Cairns received his Ph.D. in muscle physiology from the John Curtin School of Medical Research, at the Australian National University in 1991. His main research interests are on mechanisms of fatigue from the cellular level up to whole-body exercise, with a particular focus on the role of electrolytes, excitability and motor drive in skeletal muscle fatigue. He was the New Zealand Olympic table tennis coach in 2004. He is currently working as an Associate Professor in the School of Sport and Recreation, Faculty of Health and Environmental Sciences, AUT University, Auckland, New Zealand.

Notes

Note: pathways linking the various brain centers are speculative.