Sleep has long been regarded as an important step in the regeneration and rehabilitation of our physical and mental capabilities. Sleep takes up about a third of a stable adult's life (Lee, 1997). Despite the fact that we all know that sleep is the most important part of healing, all of us, including athletes, seem to overlook its significance (Walters, 2002).
Based on research, athletes often experience sleep difficulties and generally have lesser sleep compared to non-athletes (Walters, 2002). Fatigue levels will rise, resulting in a reduction in work capability. As a result, an athlete's success can deteriorate, reducing the efficacy of a training program (Gunning, 2001). As such, to perform well during trainings and competitions, an athlete must have proper sleep and optimal rest.
So what is Sleep?
According to Dr. Kathryn A. Lee in her research on sleep and common sleep problems, sleep is defined as a natural and regular period of inactivity whereby our consciousness is ceased, body functions are slowed down and responses to external stimuli are reduced (Lee, 1997).
Sleep is divided into two broad types: Non-Rapid Eye Movement-sleep (NREM) and Rapid Eye Movement-sleep (REM). It is further categorized into three distinct stages of Non-REM, which exist in a spectrum from "relaxed" wakefulness in N1 to "light" sleep in N2 and "deep" sleep in N3 (Carskadon & Dement, 2011)
What is Heart Rate Variability?
HRV is a non-invasive measuring instrument that studies the differences in intervals between each heartbeat when people are in various circumstances. It's been shown to be effective in detecting acute fatigue and responding to physical demands. (Achten & Jeukendrup, 2003).
The autonomous nervous system (ANS) is normally in charge of modulating the variations (Sztaizel, 2004). The automatic activation of the sympathetic and parasympathetic pathways regulates two variables: resting heart rate (RHR) and heart rate variability (HRV) (Michels et al., 2013). When we are stressed, our sympathetic function increases, causing a rise in heart rate and a decrease in HRV. As a result, the level of activation in our parasympathetic or sympathetic pathways is influenced by the strength (relaxed or stressful) of our environment (Boudreau et al., 2013).
So what is the link between sleep quality/quantity, heart rate variability, and sports performance?
Sleep aids in the body's general regeneration and healing, energy storage, memory consolidation, brain development, and immune system maintenance (Samuels, 2008).
Physiological growth and repair occur during ‘deep’ sleep (Walter, 2002). Protein synthesis and growth hormone secretion are increased while cortisol secretion is decreased (Dijk, 2009). These mechanisms tend to be highly essential for athletes who need to heal rapidly in order to restore weakened peripheral muscles (Gololobova,1961).
According to Walker and Stickgold (2005), they discovered that the learning process persists even though further practice is not available, and that this delayed progress happens while sleeping. They also studied participants who had sleep deprivation during training and then took another night of recovery sleep to see whether there was a correlation between quality sleep and sleep-dependent motor sequence learning. Their findings indicate that natural learning gains were stifled overnight (Walker & Stickgold, 2005).
Quality sleep also has positive influence on brain functioning such as brain activity patterns (Gillis, 1996). According to Sora song (2006), sleep aids in the consolidation of memory, the improvement of judgment, the promotion of learning and focus, the quickening of response times, and the sharpening of problem-solving and precision.
As a result, sleep loss has the ability to impair executive brain functions (e.g., working memory, arithmetic equations, and recall delay), which are primarily based on prefrontal cortical operation (Nilsson et al., 2005). Sports success also includes decision-making, and mistakes caused by poor sleep quality can be mirrored in performance outcomes (Reilly & Edwards, 2007).
SWS is related to body regeneration due to increased growth hormone, muscle reconstruction, bone strengthening, nervous system healing, protein synthesis, and free fatty acid mobilization (Fullagar et al., 2015). It's likely that vigorous training caused a rise in SWS to allow for proper healing (Shapiro, Bortz, Mitchell, Bartel, & Jooste, 1981). Previous study has also shown that RHR and HRV are immune to exhaustion and regeneration in endurance athletes (Buchheit, 2014).
Professor William M. Adams and colleagues studied the relationship between resting heart rate (RHR), heart rate variability (HRV), and sleep characteristics of a female collegiate cross-country team for 12 weeks and found that RHR was elevated at the end of the season compared to the start of the season (Sekiguchi et al., 2019). There was also an association between elevated RHR and increased percentage of time in SWS. Towards the end of the season, heart rate variability was lower than compared to the rest of the weeks suggesting a correlation between decreased heart rate variability and increased percentage of time spent on SWS (Sekiguchi et al., 2019).
Based on the data presented in this investigation, it was proposed that when the physiological state was impeded, there is an increase in the percentage of time spent in slow-wave sleep in order to guarantee recuperation. As such, the usage of appropriate rest techniques ought to be put in place to advance plentiful slow-wave rest when the body needs physiological rebuilding.
Recommendation to enhance performance
Since athletes' internal biological clocks are disturbed when they have an irregular sleep schedule, it is advised that they maintain a proper sleep pattern. This lengthens the time it takes the athlete to fall asleep.
A variation in our sleep cycle will also cause disruption to our circadian clock. As a result, it is the athletes' duty to determine how much sleep they need and to keep track of their sleep schedule (Walters, 2002). A time of four to five days is required for athletes to transition to a new sleeping pattern (Nicol, 1988).
The athlete's sleep and wake-up hours must be consistent to guarantee that he or she gets up at the same time every day, regardless of sleep quality the night before (Reisser, 2006).
Another recommendation is for athletes to cultivate a 10-minute bedtime routine, which acts as a stage of preparation for the mind and body to be ready for rest (Reisser, 2006). Conclusion
Athletes are typically subjected to intense, high-volume preparation while still dealing with other social stressors. As a result, sleep is critical for an athlete's physical well-being.
Sleep deficiency may have a detrimental effect on an athlete's physical health, mental well-being, and immune system. As coaches, we should teach athletes about the importance of getting enough sleep, the conditions that disrupt sleep, and how sleep affects success and rehabilitation.
Coaches should put a greater focus on an athlete's overall sleep efficiency and quantity by being more diligent in recognizing and determining the causes of sleep problems. Coaches can also aid athletes in the advancement of coping mechanisms in order to increase their optimal sleep.
Achten, J., & Jeukendrup, A. E. (2003). Heart rate monitoring: Applications and limitations. Sports Medicine (Auckland, N.Z.), 33, 517– 538. https://doi.org/10.2165/00007256- 200333070-00004.
Boudreau, P., Yeh, W. H., Dumont, G. A., & Boivin, D. B. (2013). Circadian variation of heart rate variability across sleep stages. Sleep, 36(12), 1919–1928. https://doi.org/10.5665/sleep.3230
Buchheit, M. (2014). Monitoring training status with HR measures: Do all roads lead to Rome? Frontiers in Physiology, 5, 73.
Carskadon, M. A., & Dement, W. C. (2011). Normal Human Sleep. Principles and Practice of Sleep Medicine, 16–26. https://doi.org/10.1016/b978-1-4160-6645-3.00002-5
Dijk D. J. (2009). Regulation and functional correlates of slow wave sleep. Journal of clinical sleep medicine : JCSM : official publication of the American Academy of Sleep Medicine, 5(2 Suppl), S6–S15.
Fullagar, H. H. K., Skorski, S., Duffield, R., Hammes, D., Coutts, A. J., & Meyer, T. (2015). Sleep and athletic performance: The effects of sleep loss on exercise performance, and physiological and cognitive responses to exercise. Sports Medicine (Auckland, N.Z.), 45, 161– 186. https://doi.org/10.1007/s40279-014-0260-
Gillis, A. M. (1996). Why sleep? Bioscience, 46(6): 391-395.
Gunning, L. (2001). Enhancing recovery: Impact of sleep on performance. Sports Coach, 23(1): 33.
Gololobova, M. T. (1961). 24-hour rhythm of cell multiplication in rat epidermis during healing of skin wounds. Bull Exp Biol Med 50, 1088–1090. https://doi.org/10.1007/BF00784887
Lee, K. A. (1997). An overview of sleep and common sleep problems. ANNA Journal, 24(6): 614-625.
Michels N., Clays E., De Buyzere M., Vanaelst B., De Henauw S., Sioen I. (2013). Children’s sleep and autonomic function: low sleep quality has an impact on heart rate variability. SLEEP; 36(12):1939-1946.
Nicol, R. (1988). Slaap soos ‘n droom ─ sonder pille. Kaapstad: Human & Rossouw.
Nilsson, J. P., Soderstrom, M., Karlsson, A. U., Lekander, M., Akerstedt, T., Lindroth, N. E., & Axelsson, J. (2005). Less effective executive functioning after one night’s sleep deprivation. Journal of Sleep Research, 14(1): 1-6.
Reilly, T. & Edwards, B. (2007). Altered sleep-wake cycles and physical performance in athletes. Physiology & Behaviour, 90: 274-284.
Reisser, P. C. (2006). Overcoming fatigue: In pursuit of sleep and energy. Colorado Springs, CO: Tyndale House.
Samuels, C. (2008). Sleep, recovery, and performance: The new frontier in high-performance athletics, Neurologic Clinics, 26: 169-180.
Sekiguchi Y., Adams W. M., Benjamin C. L., Curtis R. M., Giersch G. E. W., Casa D. J. (2019). Relationships between resting heart rate, heart rate variability and sleep characteristics among female collegiate cross‐country athletes. Journal of Sleep Research. 28(6):e12836.
Shapiro, C. M., Bortz, R., Mitchell, D., Bartel, P., & Jooste, P. (1981). Slow‐wave sleep: A recovery period after exercise. Science, 214, 1253– 1254. https://doi.org/10.1126/science.7302594
SONG, S. (2006). Sleeping your way to the top. Time, 167(30): 83.
Sztajzel, J. (2004). Heart rate variability: A noninvasive electrocardiographic method to measure the autonomic nervous system. Swiss Medical Weekly, 134, 514-522.
Walker, M. P. & Stickgold, R. (2005). It’s practice, with sleep, that makes perfect: Implications of sleep-dependent learning and plasticity for skill performance. Clinics in Sports Medicine, 24(2): 310-317.
Walter, P. H. (2002). Sleep, the athlete, and performance. National Strength & Conditioning Association, 24(2): 17-24.