Sleep quality and cardiac autonomic tone in competitive athletes and in a reference group of healthy individuals

In order to achieve optimal results, competitive athletes are exposed to high physical and mental demands. For this, the function of the regeneration phase is also important, to which a restorative sleep contributes significantly. However, there are indications that insomnia symptoms may occur frequently in competitive athletes due to various stressors during training and competitions. Competitive athletes (LS) and a group of healthy controls (GK) were studied with a home sleep test (HST) in order to objectively investigate sleep structure, sleep quality, and the function of the cardiac autonomic tone. An HST including 1-lead EEG, 2-lead EOG, SpO2, and 1-lead ECG (SOMNOtouch (TM), Somnomedics) was successfully performed for group LS in n = 12 subjects (age 25.1 +/- 4.3 years) and for group GK in n = 17 subjects (age 26.1 +/- 3.2 years), each containing females and males. Questionnaires were applied to assess daytime sleepiness (Epworth Sleepiness Scale, ESS), insomnia severity (Insomnia Severity Index, ISI), and symptoms for sleep apnea (actualized STOP-Bang Questionnaire, aSBF). Sleep stages were scored visually and heart rate and heart rate variability (HRV) parameters were calculated from ECG using time series analysis (DOMINO light, Somnomedics). Data analysis revealed no differences between groups LS and GK regarding ESS and aSBF, although ISI was increased in group LS compared to GK (5.7 +/- 4.1 vs. 2.4 +/- 2.0; p < 0.02). In evaluation of sleep structure, no differences were found for sleep onset latency (ESL), total sleep time (TST), and sleep efficiency (SE) as well as percentages of light (N1 + N2), deep (N3), and REM (REM) sleep. Time in bed (TIB) was increased in group LS (503.2 +/- 52.7 vs. 445.5 +/- 45.4 min; p < 0.02). Comparing group LS with group GK it was found that mean nocturnal heart rate was decreased (48.5 +/- 6.8 vs. 56.1 +/- 5.4; p < 0.01) but HRV parameters HRV standard deviation (HRV-SD) (166.0 +/- 33.2 vs. 138.2 +/- 38.7; p < 0.04), HRV-SD1 (78.8 +/- 11.7 vs. 63.2 +/- 36.5; p < 0.01), and HRV-SD2 (220.6 +/- 48.0 vs. 183.8 +/- 45.8; p < 0.05) were increased. In the group of competitive athletes studied, some evidence of mild insomnia was found but objectively measured sleep structure did not differ from those of healthy controls. The TST, with a mean of 6.8 h in both the LS and the GK group, is lower than the sleep duration recommended by the professional societies American Academy of Sleep Medicine (AASM), Sleep Research Society (SRS), and National Sleep Foundation (NSF) for young adults. In contrast, cardiac autonomic regulation during sleep was significantly better in group LS than in the group GK and is in agreement with findings from 24-hour Holter ECG studies. The development of objective, mobile, and non-obtrusive measurement methods simplifies the assessment of sleep structure and concomitant characteristic autonomic parameters and therefore could be increasingly used in personalized health and performance management in competitive athletes.