Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
©Journal of Sports Science and Medicine (2021) 20, 778 - 788   DOI:

Research article
Relationships between Heart Rate Variability, Sleep Duration, Cortisol and Physical Training in Young Athletes
Christina Mishica1, , Heikki Kyröläinen1, Esa Hynynen2, Ari Nummela2, Hans-Christer Holmberg3, Vesa Linnamo1
Author Information
1 Faculty of Sport and Health Sciences, University of Jyväskylä, Jyväskylä, Finland
2 KIHU – Research Institute for Olympic Sports, Jyväskylä, Finland
3 Department of Health, Education and Technology, Luleä University of Technology, Luleå Sweden

Christina Mishica
✉ Faculty of Sport and Health Sciences, University of Jyväskylä, Jyväskylä, Finland.
Publish Date
Received: 03-02-2021
Accepted: 20-09-2021
Published (online): 01-10-2021
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The aims of the current study were to examine the relationships between heart rate variability (HRV), salivary cortisol, sleep duration and training in young athletes. Eight athletes (16 ± 1 years) were monitored for 7 weeks during training and competition seasons. Subjects were training for endurance-based winter sports (cross-country skiing and biathlon). Training was divided into two zones (K1, easy training and K2, hard training). Heart rate and blood lactate during submaximal running tests (SRT), as well as cortisol, sleep duration and nocturnal HRV (RMSSD), were determined every other week. HRV and cortisol levels were correlated throughout the 7-week period (r = -0.552, P = 0.01), with the strongest correlation during week 7 (r = -0.879, P = 0.01). The relative changes in K1 and HRV showed a positive correlation from weeks 1-3 (r = 0.863, P = 0.006) and a negative correlation during weeks 3-5 (r = -0.760, P = 0.029). The relative change in sleep during weeks 1-3 were negatively correlated with cortisol (r = -0.762, P = 0.028) and K2 (r = -0.762, P = 0.028). In conclusion, HRV appears to reflect the recovery of young athletes during high loads of physical and/or physiological stress. Cortisol levels also reflected this recovery, but significant change required a longer period than HRV, suggesting that cortisol may be less sensitive to stress than HRV. Moreover, our results indicated that during the competition season, recovery for young endurance athletes increased in duration and additional sleep may be beneficial.

Key words: Recovery, endurance training, physiological stress, individual adaptations, submaximal tests, autonomic nervous system

           Key Points
  • Nocturnal HRV appears to correlate with salivary levels of cortisol in young endurance athletes.
  • Recovery during the competition season, despite a decrease in physical training, may require additional time.
  • Throughout the race season, young athletes may benefit from increased sleep.
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