Unless you’re a professional athlete, it’s not easy to squeeze in the eight hours of sleep recommended by doctors and get in enough training time to keep you fit.
It’s pretty clear from recent studies that sleep is essential—for staying clear-headed, keeping up a healthy immune system, and maintaining your edge. But then again, exercise is essential too, with all of its obvious benefits, plus the bonus of better sleep.
So if it comes down to an extra hour of training, or an extra hour to snooze before the alarm goes off, which should you choose?
Definitely sleep, according to Charles H. Samuels, medical director at the Centre for Sleep and Human Performance in Calgary. “There is no argument here,” he says. “The choice between adequate recovery and training is always on the side of recovery.”
So far, most studies on sleep and exercise have focused on how limiting or extending slumber affects performance. A 2014 study in the European Journal of Sport Science tracked the sleeping habits of elite swimmers during periods of intense training and found that early-morning start times actually hindered sleep—even when athletes went to bed early.
The downside? Athletes with limited sleep tend to report “poorer mood and higher exertion” during their training, and some studies have found that sleeping less can also mess with the body’s glucose metabolism and appetite regulation.
In a 2011 study, Cheri Mah, a researcher at the Stanford Sleep Disorders Clinic and Research Labratory, and colleagues asked Stanford basketball players to stick to their normal sleep schedules and track their play for a few weeks. Then, they upped sleep times to ten hours a night (plus some power naps) and limited alcohol intake. The result: faster sprint times, better reaction time, more accurate shooting, and a better mood.
“Often, sleep is one of the first things to be sacrificed, but it is important for proper functioning and peak performance,” Mah says. The study even suggests that getting optimal sleep is the only way to hit peak performance.
But that doesn’t mean putting all your emphasis on sleep and skipping your trail runs. You have to balance the two, changing up the intensity and frequency of your workouts and budgeting enough rest to make sure that you’re allowing your body enough time to recover. Otherwise, you risk a sloppier, less satisfying performance.
“If you feel rested and ready for a long workout, then training harder and longer that day could be worthwhile,” says David Geier, an orthopedic surgeon and former director of Sports Medicine at the Medical University of South Carolina. “If you feel really tired, especially if you have trained aggressively over the last few days, then extra sleep might be a better idea.”