Heart-rate response to sympathetic nervous stimulation, exercise, and magnesium concentration in various sleep conditions. Int J Sport Nutr Exerc Metab

The aim of this study was to clarify the mechanism of impaired exercise tolerance in chronic sleep-restricted conditions by investigating variables related to heart-rate (HR) response to sympathetic nervous stimulation. Sixteen healthy men (mean age 21.5 years) were tested in a control state, acute sleep-loss state, and chronic sleeprestricted state. Participants underwent cardiopulmonary exercise testing in each state. Their norepinephrine (NE) concentration was measured before and immediately after exercise. Intracellular magnesium (Mg) concentration was measured in a resting state. Exercise duration was shorter and the ratio of HR response to the percentage increase in NE was higher in the chronic sleep-restricted state than in the control state. Intracellular Mg gradually decreased from control to chronic sleep restriction. There was a negative correlation between peak exercise duration and the ratios of HR response to the rate of increase in NE. Intracellular Mg was positively correlated with the ratios of HR response to the increase in NE both in control and in acute sleep loss. The authors conclude that the impaired exercise tolerance in a chronic sleep-restricted state is caused by hypersensitivity of the HR response to sympathetic nervous stimulation, which showed a compensation for decreased intracellular Mg concentration. Keywords: sleep deprivation, sympathetic nervous stimulation, exercise tolerance In the field of competitive sports, athletes always take care of their physical condition, including fatigue or sleep status, and try to control it during training. It is very important to control it because it directly influences their performance. In our previous studies, oxygen uptake (VO 2 ) was decreased during exercise, as indicated by anaerobic threshold (AT) and peak VO 2 , in a state of chronic sleep restriction in young healthy participants The authors are with th