Does Sleep Affect Exercise Performance?

     Nearly everyone knows that physical activity is key to a healthy mind and body; these effects are well documented. Physical activity is known to decrease heart attack risk, lower blood cholesterol, strengthen bones, reduce the risk of some cancers, and reduce the incidence of clinical mental illness (Miko et al, 2020). A systematic review by Kelley at al in 2017 explored the relationship of exercise and sleep outcomes in adults and found similar results: that, for 950 adults, exercise improves selected sleep outcomes in adults (Kelley, 2017). These benefits are widely known; at the same time, the benefits of consistent sleep are far less understood. Sleep is known to benefit cognitive performance and relieve stress, yet its full range of effects are vastly ignored by the public. While we all know that physical activity can help us sleep in a variety of ways, such as producing melatonin and regulating body temperature, sleep is just as important in facilitating proper physical activity practices. Therefore, within the bidirectional relationship between sleep and exercise, proper sleep is paramount to staying physically and mentally healthy.

    Firstly, it is important to address the general effects of poor sleep. According to Van Someran in 2014, inconsistent sleep schedules cause long-term effects on waking attention regulation. He postulates, according to mouse research, that chronic sleep deprivation causes neuronal and cell degeneration and mitochondrial stress in brain and body areas related to arousal, such as the hypothalamus and the pons (Someran, 2014). This causes excess drowsiness at night weeks to months after the sleep deprivation, showing that this damage extends far past the range of unhealthy sleep practices. In this way, sleep deprivation across a college career could cause sleep problems years into the future. Furthermore, sleep dysregulation is related to increases in ghrelin production and decreases in leptin (Someran, 2014). By decreasing the production of the hunger-quenching hormone and increasing the production of the hunger hormone, it is clear to see how sleep loss produces a dual-cause driver of overeating and weight gain (Someran, 2014). In particular, the researchers saw that sleep loss promoted snacking behaviors throughout the day. However, this relationship goes further; disrupted sleep of any kind can cause abnormal glucose metabolism, therefore promoting an individual’s risk for diabetes and CVD (Someran, 2014). Sleep dysregulation is also linked to specific pathway dysregulations in the brain. The dopamine reward pathway in particular relies on the reproduction of its daytime activity during slow-wave sleep- when one isn’t able to reach delta wave level of sleep, these processes are interrupted. This, then, may impede the regulation of the reward-learning pathway (Someran, 2014). In conversation with the importance of exercise, this reward pathway dysregulation may hinder one’s efforts to become more physically fit, as one’s drive to exercise is heavily dependent on this same pathway. Lastly, the clearance of toxic waste in the brain is interrupted when we don’t get quality sleep. The researchers found that waste products built up in the brain from daily activity were not as effectively cleared at night when sleep was inconsistent, therefore allowing increased buildup of amyloid-beta plaques that contribute to the onset of Alzheimer’s disease (Someran, 2014).

    In terms of exercise, new research has explored the effects of sleep loss on measurable physical health metrics. A systematic review and meta analysis from Craven et al in 2022 investigated exercise performance with or without sleep loss interventions. In all of the identified studies, patients were randomized to get normal sleep or to receive less than optimal sleep (<6 hrs) per night. They were then tested for a variety of physiological performance metrics, such as strength, endurance, anaerobic power, and high-intensity intervals. They also accounted for how sleep was disrupted (at the end, beginning, or throughout) as well as the time of day that the exercise was performed. Over 226 outcome measures from 69 publications, there was a significant negative impact of sleep loss on the percent change in exercise performance of any kind (Craven, 2022). They saw that general sleep deprivation, as well as later sleep interruptions, are positively associated with worsened exercise performance metrics, measured by percentage from one’s maximum output (Craven, 2022). They only saw a significant effect, however, when exercise was performed farther away from the night of low-quality sleep; exercise performed in the morning was mostly unaffected (Craven, 2022). It is clear from this meta-analysis that sleep loss is significantly associated with worsened exercise performance, especially when it is performed in the afternoon.

    The effects of sleep dysregulation can be seen in the pursuit of healthy habits overall, as well. Kline and others in 2014 performed a systematic review on the effect of poor sleep for overall physical health habits. They reference previous studies that found a loose association between sleep struggles and lack of exercise; for example, adults with insomnia were significantly less active and had more heart problems than those with less sleep issues. They also saw this relationship play out in worsened weight, energy, and fatigue outcomes (Kline, 2014). According to two studies, Kline says, insomnia was correlated with lower levels of exercise for 2-7 years following.

    Other studies have explored the effect of poor sleep on proximal exercise habit, finding that poor sleep strongly predicts a lack of activity the following day (Kline, 2014). Furthermore, adults that preferred to wake up early had significantly more exercise habits than adults that chose to wake up later. It is possible that these results were bi-directional as well, as exercise is known to reliably shift circadian rhythm (Kline, 2014). He also notes results of three studies into CPAP treatment on patients with obstructive sleep apnea, and how these works failed to find any discernible improvements to exercise improvements (Kline, 2014). This signals, perhaps, that proximal sleep improvements may not be effective to improve exercise habits on its own. Instead, long-term consistent sleep may be necessary to obtain these benefits.

    Sleep is a vital facet to mental and physical health. Hundreds of studies across all of these articles have seen significant physical health and habit disruptions from a lack of proper sleep, a concept that has been sorely ignored by the public. Although exercise may be an important behavioral factor for fixing one’s sleep schedule, the relationship may be bidirectional: that poor sleep may be a key factor to maintaining optimal physical fitness.

Works Cited

Miko HC, Zillmann N, Ring-Dimitriou S, Dorner TE, Titze S, Bauer R. Auswirkungen von Bewegung auf die Gesundheit [Effects of Physical Activity on Health]. Gesundheitswesen. 2020 Sep;82(S 03):S184-S195. German. doi: 10.1055/a-1217-0549. Epub 2020 Sep 22. PMID: 32984942; PMCID: PMC7521632. 

Kelley GA, Kelley KS. Exercise and sleep: a systematic review of previous meta-analyses. J Evid Based Med. 2017 Feb;10(1):26-36. doi: 10.1111/jebm.12236. PMID: 28276627; PMCID: PMC5527334.

Craven J, McCartney D, Desbrow B, Sabapathy S, Bellinger P, Roberts L, Irwin C. Effects of Acute Sleep Loss on Physical Performance: A Systematic and Meta-Analytical Review. Sports Med. 2022 Nov;52(11):2669-2690. doi: 10.1007/s40279-022-01706-y. Epub 2022 Jun 16. PMID: 35708888; PMCID: PMC9584849. 

Kline CE. The bidirectional relationship between exercise and sleep: Implications for exercise adherence and sleep improvement. Am J Lifestyle Med. 2014 Nov-Dec;8(6):375-379. doi: 10.1177/1559827614544437. PMID: 25729341; PMCID: PMC4341978. 

Van Someren EJ, Cirelli C, Dijk DJ, Van Cauter E, Schwartz S, Chee MW. Disrupted Sleep: From Molecules to Cognition. J Neurosci. 2015 Oct 14;35(41):13889-95. doi: 10.1523/JNEUROSCI.2592-15.2015. PMID: 26468189; PMCID: PMC4604227.