Abstract
A reliable non-invasive method to assess autonomic nervous system activity involves the evaluation of the time course of heart rate variability (HRV). HRV may vary in accordance with the degree and duration of training, and the circadian fluctuation of this variable is crucial for human health since the heart adapts to the needs of different activity levels during sleep phases or in the daytime. In the present review, time-of-day and chronotype effect on HRV in response to acute sessions of physical activity are discussed. Results are sparse and controversial; however, it seems that evening-type subjects have a higher perturbation of the autonomic nervous system (ANS), with slowed vagal reactivation and higher heart rate values in response to morning exercise than morning types. Conversely, both chronotype categories showed similar ANS activity during evening physical tasks, suggesting that this time of day seems to perturb the HRV circadian rhythm to a lesser extent. The control for chronotype and time-of-day effect represents a key strategy for individual training schedules, and, in perspective, for primary injury prevention.
Highlights
The way in which the cardiovascular system responds to exercise stress has captured the imagination of sport scientists over the past century [1]
These variations include circadian variations during the course of the day, which could have either a positive or negative effect on sport performance [3]. For this reason, understanding the interactions between cardiovascular function, activity of the autonomic nervous system (ANS), chronobiology, biological rhythms, and chronotype allows to us understand the effects of exercise on human performance. The aim of this narrative review is to discuss the circadian pattern of heart rate variability (HRV) and the effect of time-of-day and chronotype on HRV circadian rhythm in response to acute physical activity
Vigo et al, [76] demonstrated that state slow-wave sleep is characterized with increased HRV, whereas rapid eyes movements (REM) sleep is associated with increased linear HRV in all frequency components. They observed that during the slow-wave cycle, HRV was characterized by high-entropy VLF and increased relative amplitude in the high frequency power (HF) component with rapid eye movement sleep that were indistinguishable from the wake phase with respect to nonlinear HRV, and were associated with increased linear HRV globally and all its frequency components
Summary
The way in which the cardiovascular system responds to exercise stress has captured the imagination of sport scientists over the past century [1]. Critical adjustments are continually made by the cardiovascular system to meet the diver’s demands with respect to the musculature and the heart [2] These dynamic adjustments in cardiac and peripheral vascular control, including their regulation by the autonomic nervous system (ANS), occur in response to rapid changes in the heart rate (HR) and blood pressure. People with a strong predisposition toward eveningness reach their best performances later in the day: E-types seem to have more of an advantage and to be less fatigued in the second part of the day than N- and M-types [35,36,37,38] It seems that the chronotype could play a key role in determining the circadian expression of the human body clock in different conditions and settings
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