Most athletes would agree that getting enough sleep is important for optimal sports performance, but until recently this was just a theory without much evidence to back it up. But now researchers are discovering just how much sleep deprivation can impact athletic performance. Sleep researchers are discovering that sleep deprivation can have a big impact on our basic metabolism and not getting enough sleep slows glucose metabolism by as much as 30 to 40 percent.
Sleep Deprivation Inhibits Glucose Metabolism, Decreases Endurance
Eve Van Cauter, Ph.D., from the University of Chicago Medical School, studied the effects of three different durations of sleep in eleven men aged 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.
What Does the Research Mean for Sleep-Deprived Athletes?
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 toovertraining 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.
It is the alternation of adaptation and recovery that takes the athlete to a higher level of fitness. High-level athletes need to realize that the greater the training intensity and effort, the greater the need for planned recovery. Monitoring your workouts with a training log, and paying attention to how your body feels and how motivated you are is extremely helpful in determining your recovery needs and modifying your training program accordingly.
Spiegel, Leproult and Van Cauter, Impact of sleep debt on metabolic and endocrine function.The Lancet (1999;354:1435-1439).
Fullagar HH, Skorski S, Duffield R, Hammes D, Coutts AJ, Meyer T.. Sleep and athletic performance: the effects of sleep loss on exercise performance, and physiological and cognitive responses to exercise. Sports Med. 2015 Feb;45(2):161-86. doi: 10.1007/s40279-014-0260-0.