Athletes and Sleep Issues: New Insights Into Translating Laboratory Findings in a Real-World Setting

Sleep is vital in accelerating recovery processes, enhancing performance, and maintaining good health, for all human beings and particularly for athletes. Habitual sleep deficit (sleep duration <6 hours) has been associated with major health problems in the general population. ¹⁴ Laboratory studies have shown that acute total sleep deprivation (i.e., no sleep for a whole night) or severe sleep restriction impairs muscle recovery as a result of sleep debt’s effects on catabolic and anabolic hormones.^5,6,15 In addition, sleep deficit may increase circulating markers of inflammation. ⁵ Besides health, it is well documented that either acute sleep deprivation or acute severe sleep restriction can significantly compromise human performance the subsequent day in exercise tasks requiring skill, anaerobic power, strength, and endurance. ³

Athletes appear vulnerable to sleep loss due to training and nontraining stressors. It has been recommended that competitive athletes should get 9 to 10 hours of nocturnal sleep to ensure adequate recuperation, ¹³ or 8 hours 50 minutes of nighttime sleep to feel rested. ¹⁶ These recommendations notwithstanding, athletes often get 2 to 4 fewer hours nighttime sleep than recommended and 1 to 3.5 fewer hours nighttime sleep compared with the amount required to feel rested.^11,12

To date, the influence of sleep loss on recovery, health, and performance has been examined mostly in well-controlled laboratory conditions, where physically active or recreational athletes participate in experimental conditions requiring them to undergo sleep deprivation, early sleep restriction (i.e., to remain awake until a predetermined hour in the night and to sleep thereafter), or late sleep restriction (i.e., going to bed at a regular time, waking-up earlier than usual, and staying awake thereafter). Despite their importance, such laboratory findings may not replicate what happens in an athletes’ life and, thus, transferring such findings to a real-world sport setting is questionable. In the present editorial, we aim to identify gaps between laboratory findings and the real-life stressors making athletes vulnerable to sleep loss. Further, we shed light on methodological constraints hindering the transfer of existing evidence in a real-world athletic setting, stimulating further research on this growing and promising area of research.

Do Athletes Get Insufficient Total Sleep During a Day?

A growing number of studies suggest that athletes get lower amounts of nighttime sleep than they need. Engagement in multiple and demanding training sessions and competitions may induce psychological, mood, and endocrine disturbances; arousal; and muscle soreness, which may disturb subsequent nighttime sleep. ⁸ It was found recently that intensified Olympic preparation provokes sleep interruptions, increases morning salivary cortisol, and decreases perceived recovery. ² Nevertheless, sleep disturbances were not found in other studies employing nonelite athletes, possibly because a compromise in mean sleep duration and/or efficiency is likely caused by the extremely high training loads and other stressors that are often applied in an elite sport setting. ⁷ It appears unlikely that increases in training loads contribute to poor sleep in lower-level athletes, unless they train above a critical “threshold.”

In addition, frequent traveling that requires either early or late sleep restriction, training schedules requiring early morning or late evening training/competition, and social obligations are predisposing factors contributing to insufficient nighttime sleep. Regardless, short-term recording of “baseline” values has shown that professional athletes generally sleep less than recommended, and that this might be linked to social commitments that do not allow time for sufficient sleep or to the fact that proper and applied sleep strategies have not yet been implemented or even advised. A closer look at athletes’ sleep behavior, however, reveals that they do get less nighttime sleep, but that this may be counteracted by taking long midday naps. ¹

Pros and Cons of Laboratory Studies: What Have They Already Shown?

Thus far, the adverse effects of sleep loss on health, exercise performance, and recovery indices have been well documented. It is known, for instance, that a single night of sleep deprivation increases resting blood interleukin-6 concentration the following day. ¹⁵ Accordingly, acute or sustained sleep deprivation has been shown to impair exercise performance and muscle recovery, ¹⁵ and to modify inflammatory and hormonal markers following training. Notably, however, in most of these studies, the subjects employed were not athletes, making implementation of the results in sport settings challenging.

There are several reasons why existing sleep restriction protocols do not imitate what really happens in an athletes’ life. The first is related to the nature of the protocols. Indeed, most sleep experiments (e.g., Rae et al, ¹⁵ Dáttilo et al ⁵ , and Cullen et al ⁴ ) have been applied in well-controlled laboratory settings and not in the participants’ homes. Although sleep recording in the artificial sleep room of a laboratory provides valuable information concerning not only basic sleep patterns (actigraphy), but also sleep stages, it is likely that sleep behavior may alter when sleeping in an unusual environment is enforced, let alone the effects of the specific equipment attached to participants’ head/eyes while sleeping (e.g., encephalography measures). As a consequence, the practical significance of experimental findings obtained in a laboratory sleep room is likely to be poor due to the relatively low ecological validity of the experiments.

Second, most existing studies have employed healthy and active people with normal sleep duration (i.e., 8 hours of habitual nocturnal sleep) or recreational athletes, but not elite-level athletes. In fact, elite athletes may present erratic sleep patterns, ⁹ and inadequate nighttime sleep duration and quality. In addition, elite athletes have been found recently to take long midday naps (45-124 minutes),^11,12 most likely to counteract the nighttime sleep deficit, accelerate recovery, and reverse any sport-performance decline. ¹ Indeed, observational studies have demonstrated that, due to training/competition stressors and social or educational commitments, athletes participating in various sports often report poor habitual nighttime sleep quantity (<7 hours), ¹⁰ and, in some cases, low sleep quality. ¹⁰

Third, the sleep restriction/deprivation protocols used currently require either total or severe sleep deprivation (e.g., 50% reduction of normal sleep duration or half the duration of the total time in bed), which is not common in an athletes’ life. Although poor nighttime sleepers, athletes rarely remain awake for a whole night, and also rarely obtain less than 50% of the sleep they need during the day. However, for the above-mentioned reasons, athletes may suffer from mild, but chronic, sleep deficit (20% to 40% less than required). We are currently not aware of the influence that mild chronic sleep deficit has on health, recovery, and the performance indices of athletes.

Unlike laboratory experiments, where participants have been found to obtain sufficient habitual nocturnal sleep, athletes habitually receive less nocturnal sleep than required. Since poor habitual sleep duration (i.e., <6 hours of nocturnal sleep) may induce physiological adaptations of unknown mechanism, the adverse effects of acute sleep restriction on athletes’ exercise performance are expected to be insignificant or negligible, but still unidentified.

Future Directions

Considering the abovementioned gaps, we suggest sport scientists and researchers consider the following research directions:

1. We need more data from elite/world-class athletes. Caliber of competition is a factor to consider when investigating athletes’ sleep. Elite athletes are accustomed to increased training loads, stressful sport events, nighttime matches, and frequent traveling, all of which have been found to suppress sleep. It is unknown whether elite athletes present a different time course of recovery following insufficient sleep. Along these lines, it is expected that, compared with competitive or recreational athletes, elite athletes would present different sleep patterns and architecture, (including mid-day naps), and likely unchanged exercise performance.

2. Longitudinal observational sleep studies combining modern, home-based sleep measures are necessary. It is known that sleep behavior may change in response to several circumstances in a person’s life. Since most existing sleep data have been derived during short-term (e.g., 7-20 days) observations, it is prudent to seek longitudinal observations describing how, and whether, sleep changes in different phases of a sport season. In this context, actigraphy, together with modern, home-based polysomnography recordings will help bridge the gap between laboratory and field settings.

3. Sleep measures should be included in machine-learning forecasts. Besides objective sleep measures, other crucial parameters (injury/illness incidence, exercise performance, and objective and subjective recovery indices), which have been found to be interrelated with sleep, would be useful to record. In such a scenario, comprehensive training and wellness data should be inserted into machine learning for the prevention of health issues and for performance forecasting.

4. Proper advice and implementation of effective sleep strategies are essential for athletes’ health and performance. Despite the need for efficient sleep strategies, and the fact that some studies have shown promising results, we still have a long road to travel to implement efficient sleep strategies in athletes.

—Petros G. Botonis, PhD
School of Physical Education and Sports Science, National and Kapodistrian University of Athens

—Maria Grammenou, PhD
Institute of Sports and Preventive Medicine, Saarland University

—Argyris G. Toubekis, PhD
School of Physical Education and Sports Science, National and Kapodistrian University of Athens