Introduction
Public health guidelines widely endorse exercise as a vital lifestyle intervention to enhance sleep health and reduce risk of chronic disease. The relationship between physical activity and sleep is bidirectional and multifaceted, involving physiological mechanisms such as thermoregulation, mood regulation, metabolic expenditure, and circadian rhythm synchronization. However, strenuous exercise performed close to bedtime may provoke heightened sympathetic nervous system arousal, potentially disrupting subsequent sleep initiation and maintenance. Traditional sleep hygiene guidelines have thus typically discouraged intense physical activity within hours of bedtime. Yet, recent meta-analyses report minimal adverse effects of evening exercise when intensity or duration are assessed individually, prompting the need to examine the combined impact of exercise intensity and duration—conceptualized as exercise strain—on sleep and related autonomic parameters.
