An article from the National Sleep foundation (NSF) states that "if you are experiencing sleep deprivation, your athletic performance may suffer."
Some effects of sleep deprivation may strike at the body, causing reduced endurance and a drop in the fitness level. Eyesight and hearing may be impaired. Other effects are emotional, including mood swings.
Logic would say that getting enough sleep is important for optimal sports performance, but there wasn't much evidence to support this theory -- until recent studies found that sleep deprivation can slow glucose metabolism by as much as 30 to 40%.
Eve Van Cauter, Ph.D., from the University of Chicago Medical School, studied the effects of three different durations of sleep in 11 men ages 18 to 27. For the first three nights of the study, the men slept eight hours per night; for the next six nights, they slept four hours per night; for the last seven nights, they slept 12 hours per night.
Results showed that after four hours of sleep per night (the sleep deprivation period), they metabolized glucose least efficiently. Levels of cortisol (a stress hormone) were also higher during sleep deprivation periods, which has been linked to memory impairment, age-related insulin resistance, and impaired recovery in athletes.
Van Cauter said that after only one week of sleep restriction, young, healthy males had glucose levels that were no longer normal and showed a rapid deterioration of the body's functions. This reduced ability of the body to manage glucose is similar to those found in the elderly.
Most of what we know about sleep deprivation has to do with immune function and brain function. This study is interesting because it shows that sleep deprivation can negatively impact physiology that is critical for athletic performance -- glucose metabolism and cortisol status. While no one completely understands the complexities of sleep, this (and other research) indicates that sleep deprivation can lead to increased levels of cortisol (a stress hormone), decreased activity of human growth hormone (which is active during tissue repair), and decreased glycogen synthesis.
Other studies link sleep deprivation with decreased aerobic endurance and increased ratings of perceived exertion.
What does this all mean?
Glucose and glycogen (stored glucose) are the main sources of energy for athletes. Being able to store glucose in muscle and the liver is particularly important for endurance athletes. Those who are sleep deprived may experience slower storage of glycogen, which prevents storage of the fuel an athlete needs for endurance events beyond 90 minutes.
Elevated levels of cortisol may interfere with tissue repair and growth. Over time, this could prevent an athlete from responding to heavy training and lead to overtraining and injury.
Obviously, more research is necessary. But this study indicates that a chronic lack of sleep may affect metabolic function. For the endurance athlete, proper sleep during heavy training and before competitions certainly may help and is unlikely to cause harm.