Anxiety causes many athletes to sleep poorly the night before a major competition, and if they have crossed more than a couple of time zones in order to compete, actual sleep may be limited to just an hour or two. Some elite athletes claim that they have set personal bests after a night of tossing and turning, but the prevailing view is that poor sleep tends to lead to poor performances. What is the true effect of sleepless nights on competitive capacity, and should athletes worry if they chalk up only an hour or two of sleep the night before a major event?

One problem in working out how sleep deprivation influences exercise capacity is that scientists don't completely understand sleep itself. It is clear, however, that sleep can be divided into five distinct stages: stages 1-4 consist of non-rapid-eye-movement sleep; during a normal night of sleep, these are usually followed by the rapid-eye-movement (REM) stage of sleeping (stage 5). Scientists who specialise in sleep maintain that during a night of normal sleep, REM and non-REM sleep stages repeat in cycles lasting about one-and-a-half hours, although age and the amount and quality of sleep on previous nights can alter this pattern.

Since stages 3 and 4 of sleep produce brain waves which have a slow frequency, these stages are referred to as 'slow-wave' sleep. As it happens, slow-wave sleep is critically important for athletes, because it is when 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; it is thus one of the key hormones which help athletes recover from tough workouts and also improve physiologically in response to training. Studies show that when an athlete loses sleep (particularly slow-wave sleep), growth-hormone release from the pituitary gland diminishes. This may be a key reason why extended sleep loss can lead to decrements in physical capacity.

The physical and mental effects of missing out on sleep
But how much sleep do you actually have to miss in order to degrade your ability to lift weights, diminish your pedal-pushing power or slow your swimming speed significantly? Research reveals that as little as 20 hours of sleep deprivation can impair mental performance, but the amount of sleep loss required to damage physical prowess is less certain. What is known is rather startling, suggesting, as it does, that the physical functioning of the human body is relatively unaffected by sleep loss.

For example, after a total of 60 consecutive hours without sleep, many individuals find short, intense workouts no harder than usual. After 30 hours of sleep deprivation, athletes doing long workouts consume oxygen at the same rate, with heart rates that may actually be lower than usual, although they feel sleepy and fatigued and may report that the training session feels harder.

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 he or she can sustain a particular intensity of exercise without stopping) by an average of about 10-11% at a moderately hard intensity of about 80% VO2max (87% of maximal heart rate). 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!

Some of the research on sleep loss and performance has been a bit contradictory. For example, one investigation showed that sleep loss diminished the ability to produce peak power while exercising (ie when sprinting for home at the end of a race, accelerating up hills while cycling, or churning the water during a 200m swim event), in part by lowering maximal heart rate. 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). Not surprisingly, vertical jumping ability and isokinetic strength tend to deteriorate with sleep deprivation.

However, studies show that in spite of these negative effects, sleep deprivation extending as long as 64 hours does not necessarily damage 100m dash performance, nor decrease isometric muscle strength. The other good news is that most athletes do not actually stay awake for 30-60 consecutive hours, which is the kind of sleep deprivation most closely linked with losses in physical performance. It's much more common for anxious or time-zone-challenged athletes to get a little sleep - even if it is only 2-3 hours - during the night (or nights) before important events. And scientific research relating to sleep patterns like this is actually very reassuring.
For example, studies show that if an athlete sleeps only 2.5 hours per night for three consecutive nights, there is absolutely no loss in hand and arm-muscle strength, no decrease in broad jumping ability, no increase in perceived exertion during strenuous exercise, no decline in lung function or respiratory capacity, and - most importantly - no loss of endurance capacity. It is true that total anaerobic capacity may decline a little in such circumstances, which would have the strongest impact on athletes taking part in continuous competitive events lasting four or five minutes, or less. The loss is actually fairly small, but even a few hundredths of a second can make a significant difference to how an athlete places in a very competitive race. In other words, limited sleep can have a small but important effect on high-intensity performance.

Interestingly enough, scientists have found that body temperature 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. Although sleeplessness tends to keep the body cool, body temperature actually rises faster during exercise when athletes are sleep-deprived. Thus, loss of sleep might increase the risk of heat illness when exercising on hot and/or humid days.

The good news is that research indicates that the problem most often experienced by athletes - just one night of almost total sleeplessness before a major event - is unlikely to hurt performance. True, if you think you will perform more poorly after such a night, you probably will, but the point is that there is no real reason for you to think that way! The scientific evidence suggests that you'll still have a great chance to achieve your best-ever performance - even if you have just set a personal record for tossing and turning in bed the night before your big event.

Owen Anderson