Why Hard Training Puts Us to Sleep, or Not

Some amateur athletes have a hard time getting to sleep after a workout. Others do not. In fact, really tough workouts seem to send many athletes straight off to dreamland. What’s that about? The New York Times begins its report on the phenomenon by telling us that the science behind that sleepiness is poorly understood. In fact, the paper reports, there are no large group studies of the sleep needs of endurance athletes.
It is true, the Times reports, that sleep specialists often tell people with insomnia to exercise five
to six hours before bedtime. That’s because the mild exercise raises the body’s core
temperature, and when the temperature falls again a few hours later, that
signals the body to sleep. But what happens to
marathoners-in-training, who often find themselves sleeping 10 hours a night, requires another explanation. For that the Times turns to Dr. Alex Chediak, president of the American Academy of Sleep Medicine and chief of the Sleep Disorders Center at Mount Sinai Medical Center in Miami Beach.  One possibility,
Dr. Chediak said, is that cytokines — hormones that signal the immune
system — are making these athletes sleep so much. Exercise, Dr. Chediak said, prompts muscles to release two cytokines, interleukin 6 and tumor
necrosis factor alpha, that make people drowsy and prolong the time
they remain sleeping. In fact, those cytokines also are released when
people have a cold or infection, which is why people sleep so much when
they are ill. The Times reports that the single most important factor
for increasing the release of those two cytokines is increasing the
duration and intensity of exercise, Dr. Chediak said. And, he noted,
that’s what is happening when endurance athletes train. “A sprint will
not get you as great an effect,” he said. On the other hand, he cautioned, the cytokine hypothesis is based on extrapolations from other data and animal studies. Read more in the New York Times.