A healthy brain is humankind’s greatest asset, the most advanced product of evolution that regulates nearly all our body’s physiological functions, including athletic performance. And sleep is one of the very few things that influence brain health. Let's see how.
Sleep Increases Cognitive Performance
It has long been known that sleep deprivation deprives people of their cognitive abilities nearly to the point of a drunken state. In a study of college student-athletes, just one night of not sleeping has been found to slow reaction time by 15% in a computer task compared to baseline. Similarly, in another study involving handball goalkeepers, sleep loss of 3-4 hours for one night is enough to worsen measures of reaction time and attention by 30-50% compared to baseline.
(Baseline results were taken when participants slept usually.)
While sleep deprivation impairs cognition, the opposite is also true: Restful sleep does wonders for one’s cognitive abilities.
For instance, a study put university basketball players on a 5-7-week sleep extension program, where sleeping hours were increased from an average of 6 to 8 hours. At the end of the program, their reaction time quickened by about 15%; their performance in sprint time, free throws, and three-point field goals also improved significantly by 0.7-second, 9%, and 9.2%, respectively. The athletes also reported that the sleep extension program boosted their overall mental well-being.
Similarly, in professional baseball players, increasing sleep for one hour/night for five nights has been shown to improve response time by 13% and decrease tension and fatigue by 30-40%. These effects were absent in the control group, who still sleep 6-7 hours/night .
Even in normal young adults, proper sleep of 8-9 hours per night has been shown to keep cognitive abilities (e.g., reaction time, alertness, and mood) in top shape. Many other studies have found that even a 10-30-minute nap following a night of lack of sleep could make a difference in enhancing grip strength, sprint time, reaction time, short-term memory, and alertness in those with insufficient sleep.
The effects of sleep on cognition also have a neurobiological basis. The hippocampus, a brain region essential for memory, reactivates during sleep to reconsolidate memory and learning experiences gained during the day. Sleep also refreshes neurons in the brain, allowing neurons to process information more efficiently the next day. This effect is particularly evident in the prefrontal cortex, a brain region with high bioenergetic demand that enables higher-order cognitive functions.
So, athletes who always have to learn and master complex motor and tactical skills should keep their hippocampus and prefrontal cortex pristine.
Sleep Decreases Injury
We now know that sleep-deprived athletes are less alert with slower reaction times. Not only does this impairs athletic performance, but it also increases the risk of injuries. Athletes participate in vigorous and strenuous training and competition, so alertness to physical danger is also of utmost importance.
Besides the brain, let us not forget that sleep restores the physical body too:
- Sleep loss can blunt the complete renewal of muscle glycogen stores.
- Growth hormone secretion from the hypothalamus and pituitary gland in the brain reaches its peak during deep sleep. Growth hormone promotes muscle recovery and hypertrophy (or growth), so sleep loss will hamper such processes.
- Insufficient sleep has long been known to increase cortisol and decrease testosterone levels, leading to a state of muscle catabolism (or breakdown).
- Sleep activates the parasympathetic (rest and digest) nervous system, counterbalancing the sympathetic (fight or flight) nervous system. Therefore, sleep loss could over-activate the sympathetic system in a manner similar to overtraining.
These biological intricacies simply mean that muscles also need sleep to function optimally. Without it, muscular performance gets compromised, and the risk of injuries heightens.
Several studies have, indeed, reported that sleep-deprived people are more prone to injuries during exercise. A 2019 meta-analysis screened the sports science literature and identified seven relevant studies. Pooling the data together, the meta-analysis calculated a 60% increased risk of sports injuries among adolescents with poor sleeping habits compared to adolescents who slept well.
A 2020 study tracked the sleeping patterns of elite soccer players for six months. Results revealed that those with sub-par sleeping quality had an average of 2.5 injuries and 17.5 days of lost training days due to injuries over the six-month period. These numbers were only one injury and 2.5 days in those with satisfactory sleep quality. Another 2020 study has also found that one hour more sleep decreased the risk of injuries by 43% the following day among collegiate basketball athletes.
Overall, sleep might as well have made or stumbled an athlete’s career. After all, injuries can be severe and life-long, so there is no reason not to take precautions by sleeping well.
Sleep Enhances Visual Acuity
Recall that sleep can hurt or enhance cognitive capabilities, and one of our cognitive functions is visual acuity, the ability to see sharply and with clarity.
The brain’s visual system (the thalamocortical system) disengages from the sensory environment during sleep and reactivates when the eyes perceive light the next morning. Unrested thalamocortical system thus compromises visual functions due to inefficient neural processing. The same applies to ciliary muscles that control the shape of the eye lens. Overexerted ciliary muscles from lack of sleep will impair the lens's focusing power, resulting in blurred vision.
Multiple studies have reported that poor sleep correlates with visual impairment (including low visual acuity), an effect that is independent of age, sex, wealth status, and other socio-demographic factors. Athletes are no exception. In a study of physically fit university students, sleep deprivation for a few nights slowed their reaction time and visual search time. Another study examining handball goalkeepers also reported similar results: 3-4 hours of sleep loss for one night decreased their visual search performance by 15-30%.
Specifically, the visual search task the studies used is designed to measure visuospatial abilities, where participants have to identify the correct objects out of other random ones as fast as possible. If short-term sleep loss is sufficient to slow down the recognition of static objects, as these studies have shown, the effect should be even worse for moving objects.
Therefore, athletes with poor sleeping habits may have been compromising their visual system. They may not perceive the ball as fast as they should be, for example, slowing down reaction time as well, or they may not see the ball as clear or sharp due to blurred vision or tired eyes.
Everyone knows that sleep is a need, which is especially true for athletes. Sleep not only ensures a healthy body but a healthy brain as well. And the brain is just as important as the muscles for athletic performance, as this article has explored. In brief, proper sleep of at least eight hours per night enables top-notch cognitive abilities, such as reaction time, memory and learning, alertness, mental state, and visual acuity, while also reducing the risk of injuries. Simply put, athletes have much to gain from those 1-2 hours of extra sleep.
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