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 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.
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.
Other helpful ways to get enough rest without taking days off include:
- Get More High Quality Sleep
- Perform Active Recovery after your workouts
- Crosstrain with a completely different activity such as yoga, stretching, or going for a walk on your day off.
- Have a Massage on your rest day to help reduce muscle aches, pains and soreness.
- Get Adequate Sleep
- Eating for Sports Performance includes getting enough of the right calories for your training intensity and your individual requirements.
- Eating Before Competing - the Pre-Exercise Meal
- Eating for Recovery - the Post-Exercise Meal
Spiegel, Leproult and Van Cauter, Impact of sleep debt on metabolic and endocrine function. The Lancet (1999;354:1435-1439).