Sleep deprivation significantly impairs endurance performance. Much of the research correlating sleep loss and impaired performance has focused on the impact of cortisol, the body’s primary stress hormone. Cortisol is a powerful catabolic agent that, among other effects, increases muscle protein degradation. Chronic sleep loss increases cortisol levels. When muscles are pushed into a catabolic state by cortisol, recovery is impaired and endurance performance suffers.
As bad as that may seem, it appears that sleep deprivation hits endurance athletes with a double whammy. Not only is there increased muscle protein breakdown but, a new study shows there is also a decrease in muscle protein synthesis. Using a crossover design, 13 subjects underwent a night of total sleep deprivation that was followed at least four weeks later by a night of normal sleep. Researchers found that acute sleep deprivation decreased muscle protein synthesis by 18%. What was extremely surprising, is these results were seen after a single night of total sleep deprivation. The fact that these changes appear so rapidly may explain some of the changes to body composition that occur following periods of chronic sleep deprivation.
These results reemphasize why adequate sleep is a vital component of an effective training program.