Effects of exercise intensity on recovery of autonomic nervous system immediately after exercise and during sleep, and on subjective and objective sleep quality

Abstract

Syväoja, Heidi. 2010. Effects of exercise intensity on recovery of autonomic nervous system immediately after exercise and during sleep, and on subjective and objective sleep quality. Master´s thesis in Exercise Physiology. Department of Biology of Physical Activity. University of Jyväskylä, 90.

The exercise can be considered as a one form of stress, because it induces marked changes in the autonomic regulation of heart rate (HR). During acute exercise, parasympathetic activity decreases and sympathetic activity increases. Parasympathetic activity declines a lot or even disappears, when the exercise intensity is high. After acute exercise cessation, fast changes occur in the cardiac function within few minutes: parasympathetic tone increases, whereas sympathetic activity decreases. However, how fast the vagal reactivation is, and how long autonomic regulation of HRV is disturbed after different exercises is not well known. In addition, exercise has beneficial effects on health. It may improve the sleep duration and quality, especially the amount of slow way sleep. The purpose of the present study was to find out how an acute exercise affects the recovery of the ANS. More specifically, how different exercise intensities affect recovery of heart rate variability (HRV) immediately after exercise and during sleep. In addition, the second purpose of the present study was to investigate how exercise intensity affects the subjective and the objective sleep quality during the nocturnal sleep.

Sixteen healthy moderately active men aged 36 years participated in the study. The subjects performed moderate intensity (60 % of VO2max) and high intensity (75% of VO2max) exercises in a laboratory. The autonomic regulation of HRV and subjective and objective sleep quality were measured during the night before and after exercise sessions. Also biomarkers of stress from salivary samples ware measured after both nights at home. In addition, acute effects of exercise on HRV and biomarkers of stress from salivary samples were measured in the laboratory right after exercise sessions. HRV was measured with Alive heart monitor and analysed with the Firstbeat HEALTH computer software. Body movements of the subjects were detected with the Actiwatch activity monitoring system and analysed with Actiwatch activity & sleep analysis 5 –software.

During the first minute of recovery, high frequency power (HFP) was significantly higher after moderate intensity exercise compared to the values during exercise (p<0,01). During the second minute of recovery HFP was first time significantly higher after high intensity exercise compared to the values during exercise, (p<0,01). Moreover, HFP was lower after high intensity exercise than after moderate intensity exercise during the immediate recovery period (1.minute: 1,6 ± 0,9 vs. 3,6 ± 1,4 ln[ms²] (p<0,01), 2. minute: 2,1 ± 0,8 vs. 4,5 ± 1,2 ln[ms²], 5.-10. minute: 2,8 ± 1,3 vs. 6,1 ± 1,4 ln[ms²]). During the first four hours of sleep, HR was significantly higher (57 ± 8 vs. 52 ± 6, bpm, (p<0,001)) and root mean square of successive RRIs (RMSSD) significantly lower (51,0 ± 25,6 vs. 64,8 ± 34,0 ms, p<0,05) after high intensity exercise compared to the control. Actual sleep time (7:29 ± 0:40 vs. 6:56 ± 0:41 h:min (p<0,01)) and subjective sleep quality (71,3 ± 18,7 vs. 53,0 ± 23,5, p<0,05) was higher after high intensity exercise compared to the control.

It seems that vagal reactivation is quite fast after exercise and it depends on exercise intensity. In addition, the results suggest that the high intensity exercise disturb the cardiac autonomic regulation only during early sleep. According to results, the high intensity exercise may improve the sleep quality. These results suggest that the sleep after high intensity exercise is enough for overall recovery and enough to restore homeostasis.