The recommended 8-hours of quality sleep is often difficult to fit in among a hectic lifestyle and regular training. It’s often said that the rest and recovery part of training is the most important aspect of allowing your body to improve. But how does sleep affect sports performance?
One problem in working out how sleep deprivation influences exercise capacity is that scientists don’t completely understand sleep itself. What we do know, however, is that the natural sleep cycle can be divided into 5 distinct stages: stages 1-4 consist of non-rapid eye movement sleep, and stage 5 rapid eye movement (REM) sleep. During a night of normal sleep, REM and non-REM sleep stages repeat in cycles lasting aroung one and a half hours. Age and the amount and quality of sleep on previous nights can change this pattern.
Stages 3 and 4 of sleep produce brain waves which have a slow frequency and therefore these are known as stages of “slow-wave” sleep. Slow-wave sleep is an important stage of sleep for athletes because it is during this stage of sleep that growth hormone is released from the pituitary gland at the base of the brain.
Growth hormone stimulates muscle growth and repair, bone building and fat burning and is one of the key hormones to help you recover from tough workouts and allow your body to rebuild itself and improve in response to training. Studies show that when an athlete loses sleep, particularly slow-wave sleep, growth hormone released from the pituitary gland decreases. This may be the main reason for sleep loss affecting physical performance.
Most people feel nervous before a competition. Anxiety causes many athletes to sleep poorly the night before an event. Some elite athletes have set world best times after a sleepless night of tossing and turning, but many feel that poor sleep tends to lead to poor performances. But how much sleep do you actually have to miss in order to decrease your ability to pedal-pushing power or slow your running speed significantly?
Research shows that as little as 20 hours of sleep deprivation can impair mental performance. Surprisingly, studies suggest that the physical functioning of the human body is relatively unaffected by sleep loss!
In fact, one military study showed that after a total of 60 consecutive hours without sleep (that’s 2 and a half days without any sleep!) athletes completed short, intense workouts at the same heart rate and oxygen consumption, although many reported feeling sleepy and fatigued and that the session feels harder. Again suggesting that mental performance is affected before physical impairment.
Nonetheless, lack of sleep can have a negative impact on performance. Studies show that going 36 hours without sleep can decrease an athlete’s time to exhaustion (how long she can sustain a particular intensity of exercise without stopping) by an average of about 10-11% at a moderately hard intensity. However, a notable aspect of this research is that there is tremendous variability among individuals. Some athletes display large losses in performance (15% or more), others decline in capacity by much smaller amounts (less than 5%), while a few actually perform better when they are sleep-deprived!
Other research has shown that sleep loss can reduce coordination and efficiency during exercise – remember that only 20 hours without sleep is enough to impair normal mental functioning, which could lead to less efficient control of the muscles by the nervous system.
Interestingly, body’s temperature control is strongly influenced by sleep loss. Sleep deprivation tends to lower resting body temperature, which explains why individuals often feel cold after a sleepless night or several nights of poor sleep. But, although sleeplessness tends to keep the body cool, body temperature actually rises faster during exercise in a sleep-deprived athlete. So, loss of sleep may effect your performance more dramatically in hot or humid conditions as your body will have to work harder to maintain your normal body temperature.
Tiredness can accumulate as a result of life’s daily grind and isn’t necessarily related to your training load. Anything that wears you out physically or mentally during the day, or deprives you of sleep at night, is going to contribute to tiredness. Take a stressful week at work into account when planning your training for the week!
Chronic sleep deprivation can develop fairly rapidly. As the studies above illustrate, one late night is far less damaging than sleeping too little every night. Increasing the amount you train is likely to bump up your sleep requirements, so you will probably need in excess of the recommended 8 hours a night (although, everyone’s sleep requirements are different).
Sleep deprivation elevates the levels of the stress hormone cortisol, which impairs your body’s ability to repair muscle in response to training. Your ability to metabolise glucose is also effected, which can have a knock on effect on your weight and your body’s ability to store muscle glycogen. As previously mentioned, growth hormone will also be diminished which will impair your body’s ability to heal and recover from training.
On the other hand, sleeping poorly can be one of the first signs of overtraining. Awaking feeling tired and unrefreshed is a sign that your body is in need of rest and may benefit from a reduction in training for a short time. While physical performance is not impaired in the short-term by sleep deprivation, inadequate amounts of sleep in the long-term will certainly effect your ability to train and also can effect your mood. If you find your mood and sleep are effected for prolonged periods of time then you may need to consult your GP.
What Does All This Mean For Me?If you’re a 24-hour racer…
Mental performance, co-ordination and efficiency are likely to be the first effected as a result of short-term sleep deprivation. Take this into account when pacing yourself for the event – things are going to start feeling harder later on even if they’re not – and on tricky sections of the course as these will require more concentration than usual.For the more normal among us…
The good news is that research indicates that the problem experienced by most athletes – just one night of poor sleep the night before a major event – is unlikely to decrease your performance. Although, if you think you will perform more poorly after such a night, you probably will! But, beware of chronic sleep deprivation, which can be the result of the daily grind and sleeping an hour or so too little every day.
DISCLAIMER: Advice and information is provided via SheCycles.com Clinic on a free of charge basis as a supportive service to women in sport. It should not replace the use of your General Practitioner for medical problems.Copyright 2007 Dr K Hurst