Sleep Debt, Training Load, and Recovery in Athletes: An Investigation of Individualized Sleep Need and Physiological Recovery

Abstract

Introduction & Purpose

Athletes differ greatly in how much sleep they require and how their bodies react to insufficient sleep, even though sleep is regarded as an essential recovery technique in competitive sports [1,2,5]. However, most current recommendations rely on generalized sleep guidelines that may not adequately account for individual differences [1, 4, 10]. This study examined two questions among elite rowers:

• whether an individual’s accumulated sleep deficit affects physiological recovery the following day, and
• whether training late or high-intensity training late in the evening impairs subsequent sleep.

We also assessed whether athlete-specific estimates of sleep requirements provide a more accurate understanding of these effects compared to fixed recommendations [4] or sleep goals generated by wearable devices.

Methods

WHOOP and self-reported wellbeing data were analysed. To measure individual sleep debt, four methods were used:

• a novel athlete-specific sleep need derived from self-assessed well-rested nights,
• the sleep need estimated by WHOOP [9],
• a standard recommendation of 8.3 hours [4], and
• a five-day weighted cumulative sleep deficit based on (1).

Associations between sleep debt and next-day indicators — recovery (estimated by a Whoop proprietary algorithm), heart rate variability (HRV), resting heart rate (RHR), and rating of perceived exertion (RPE) — were evaluated using within-athlete Spearman correlations and linear mixed-effects models. Athlete-specific physiological thresholds were estimated using piecewise regression.

Results

Our results support other research that suggests sleep is crucial for sports recovery [5, 6]. However, they show significant athlete-specific variability in both sleep requirement and physiological sensitivity to sleep debt, in contrast to research that depends on universal sleep guidelines. While HRV and RHR responses were less sensitive, with 7/27 and 5/27 of athletes showing significant decreases and increases, respectively, among athletes with sufficient data, 15/27 showed substantially lower Recovery during sleep debt. Mixed-effects models showed that for every additional hour of individualized sleep debt was associated with 15.1 % lower next-day recovery (β = −15.08, p < 0.001), 4.34 % lower HRV (β = −4.34, p < 0.001), and 1.70 % higher RHR (β = 1.70, p < 0.001).  Piecewise regression identified athlete-specific sleep debt thresholds ranging from 0.5 to 7 hours. This supports recent recommendations that encourage individualized approaches for professional athletes [4]. According to other papers [7, 8], the impact of evening exercise on sleep appears to vary with the athlete rather than being generally harmful. Because late-night high-intensity sessions were rare in our cohort, conclusions were limited to athlete-specific analyses.

Discussion

These results imply that recovery responses to insufficient sleep are extremely personalized and cannot be well explained by general sleep guidelines. Sleep need estimates derived from an athlete's own recovery behaviour may provide a more relevant approach for identifying meaningful sleep deficits in elite sport.

Conclusion

Athlete-specific sleep demand estimations are a better way to reflect the highly subjective impact of sleep debt on recovery responses than general sleep recommendations. The limited frequency of late-night high-intensity sessions indicates that future research should include cohorts with more exposure to this training pattern; the notable variation in athlete-specific thresholds emphasizes the need for customized sleep monitoring.

References

[1] Kellmann, M., Bertollo, M., Bosquet, L., Brink, M., Coutts, A. J., Duffield, R., Erlacher, D., Halson, S. L., Hecksteden, A., Heidari, J., Kallus, K. W., Meeusen, R., Mujika, I., Robazza, C., Skorski, S., Venter, R., and Beckmann, J. (2018). Recovery and performance in sport: Consensus statement. International Journal of Sports Physiology and Performance, 13(2):240–245. Epub 2018 Feb 19. https://doi.org/10.1123/ijspp.2017-0759

[2] Kenney, W. L., Wilmore, J. H., and Costill, D. L. (2015). Physiology of Sport and Exercise. Human Kinetics, 6 edition.

[3] Matthews, M. J., Kanungo, S., Baker, R. J., and Kenter, K. (2024). Exercise physiology: A review of established concepts and current questions. Physiologia, 4(2):202–212. https://doi.org/10.3390/physiologia4020011

[4] Sargent, Charli, Michele Lastella, Shona L. Halson, Gregory D. Roach. „How Much Sleep Does an Elite Athlete Need?“ International Journal of Sports Physiology and Performance. International Journal of Sports Physiology and Performance 16, Nr. 12 (2021): 1746–57. https://doi.org/10.1123/ijspp.2020-0896.

[5] Bonnar, Daniel, Kate Bartel, Naomi Kakoschke, Christin Lang. „Sleep Interventions Designed to Improve Athletic Performance and Recovery: A Systematic Review of Current Approaches“. Sports Medicine 48, Nr. 3 (2018): 683–703. https://doi.org/10.1007/s40279-017-0832-x.

[6] Cunha, Lúcio A., Júlio A. Costa, Elisa A. Marques, João Brito, Michele Lastella, Pedro Figueiredo. „The Impact of Sleep Interventions on Athletic Performance: A Systematic Review“. Sports Medicine - Open 9, Nr. 1 (2023): 58. https://doi.org/10.1186/s40798-023-00599-z.

[7] Myllymäki, Tero, Heikki Kyröläinen, Katri Savolainen, u. a. „Effects of Vigorous Late-Night Exercise on Sleep Quality and Cardiac Autonomic Activity“. Journal of Sleep Research 20, Nr. 1pt2 (2011): 146–53. https://doi.org/10.1111/j.1365-2869.2010.00874.x.

[8] Stutz, Jan, Remo Eiholzer, Christina M. Spengler. „Effects of Evening Exercise on Sleep in Healthy Participants: A Systematic Review and Meta-Analysis“. Sports Medicine 49, Nr. 2 (2019): 269–87.https://doi.org/10.1007/s40279-018-1015-0.

[9] WHOOP. The wearable designed for lasting progress. https://www.whoop.com/ro/en/

[10] Sargent, Charli, Michele Lastella, Shona L. Halson, Gregory D. Roach. „The validity of activity monitors for measuring sleep in elite athletes“. Journal of Science and Medicine in Sport 19, Nr. 10 (2016): 848–53. https://doi.org/10.1016/j.jsams.2015.12.007.