In addition, chronic sleep loss can diminish mental function, raise blood pressure and precipitate mood disorders such as depression. Sleep-deprived individuals can experience reduced cardiovascular performance and reduced endurance. For the triathlete, the impact on performance may also be profound.
In a study published in the medical journal The Lancet, athletes who experienced six successive nights of sleep deprivation (four hours of sleep a night) demonstrated an impaired ability to use glucose. This will not only impair athletic performance but can also hinder recovery and affect the body's ability to build glucose stores for future use.
In addition, the study showed that sleep-deprived athletes also had elevated levels of the hormone cortisol when compared to controls. Prolonged elevations in cortisol may impair tissue growth and repair and, if the cortisol level persists, may increase the risk for the development of dementia and insulin resistance (i.e., diabetes) in the future. The good news is that these metabolic changes can be reversed when adequate amounts of sleep are achieved in recovery.
Additional studies have shown that extreme sleep deprivation can reduce the time to the point of exhaustion when exercising and increase perceived exertion. There's controversy over whether sleep deprivation affects heart rate during aerobic exercise, but some studies have suggested a connection between sleep deficits and an inability to achieve maximum heart rates with progressively higher workloads.
However, the evidence is largely inconclusive on whether sleep deprivation affects respiratory gas exchange, VO2 max, lactate production and anaerobic strength. Regardless of what the scientific studies show, however, I tell my patients--athlete or non-athlete--that sleep and adequate rest are essential to their health.
For some, however, avoiding sleep to train or work is not the problem, but rather they have problems sleeping. In many cases, there are medical issues that surround these sleep disorders. The National Institute of Health estimates that up to 40 million Americans have chronic sleep disorders. Individuals who have concerns about their ability to sleep at night or who have problems with daytime sleepiness should see their physician to assist in the diagnosis and treatment of a sleep disorder.
How Much Sleep do we Need?
So how much sleep should we get? The simple answer is as much as we need to feel rested; however, sometimes even this may not be enough. For those triathletes training three to four hours a day, the common adage of eight hours of sleep a night may not be enough for recovery.
However for most triathletes, eight to nine hours is probably ideal. In the modern age, the reality is that this probably doesn't and won't happen. Coming from a profession that has created an army of sleep-deprived individuals, I can tell you personally that I crave and love sleep, yet seldom do I get adequate amounts.
Anecdotally, my best workouts and races have always occurred during breaks in my training as a physician when I've been well rested. My mood is always better during these times, I find it easier to concentrate on tasks and I find life more manageable.
Training and competing in triathlon has always been an outlet for me in a sea of complex responsibilities. However, when it comes at the sacrifice of sleep, it becomes stressful and less enjoyable.
Unfortunately, sleeping has become equated with laziness and fails to find its way onto our list of priorities. This perception is skewed in a society that is preoccupied with doing too many things at once. Adequate sleep is part of that balance, and in triathlon it may be the most important choice in our preparation for the next race.
www.sleepfoundation.org (National Sleep Foundation)
Spiegel, K, et al. The Lancet. 354: 1435-1439, 1999
Dr. Polu is board certified in internal medicine. He is currently a clinical and research fellow specializing in kidney disease and transplantation at Harvard Medical School affiliated with Brigham and Women's Hospital and Massachusetts General Hospital in Boston. He has been competing in triathlons and endurance sports for 12 years.