Exertional fatigue in disorders of muscle

To the Editor: In his editorial (Feb. 7 issue)¹ Layzer concludes that little is known about the biochemistry of exercise-induced muscle fatigue. It is now becoming apparent, however, that such fatigue may be influenced by local and systemic potassium concentrations. There is a well-recognized association between muscle fatigue and hyperkalemia that is supported by the observation that beta-blocking agents may cause fatigue² and enhance exercise-induced hyperkalemia.³ Strenuous exercise on a cycle ergometer (approximately 350 W) results in a rapid increase in arterial plasma potassium concentrations, which peak at about 7 mmol per liter after about one minute,⁴ coinciding with the. .