Staying healthy is so easy, right? Log eight hours of sleep, work out for an hour a day at least five days a week, and steer clear of processed foods. But that math doesn't always add up—trying to fit in the recommended dosage of sleep and exercise, on top of all the other variables in your life (kids! work! relationships!), can seem impossible. So when you're debating the choice of lying in bed for another two hours or dragging yourself to the gym, sometimes shuteye wins.
But is that such a bad thing? After all, some mornings you just don’t feel well, or maybe you overdid it yesterday. Is it ever worth it to sleep in and skip the gym? Turns out, science still doesn't have the hard and fast answer (but if you find it, be sure to let us know!). “Both sleep and exercise are main behaviors that contribute to physical and mental health,” says Kelly Glazer Baron, Ph.D., a clinical psychologist and sleep researcher at the Feinberg School of Medicine at Northwestern University. Her research has found that clocking at least seven hours of sleep can actually help you work out longer and harder the next day. And the exercise/sleep equation goes both ways—people with insomnia who started a regular aerobic exercise program improved the quality of their sleep and felt less tired during the day, another study from Northwestern University found. (You should also be aware of The Unhealthy Food Cravings Caused by Just One Less Hour of Sleep.)
Considering multiple studies point to the direct relationship between sleep and exercise, there's no denying that you should strive for adequate amounts of both, adds Shannon Fable, director of exercise programming at national gym chain Anytime Fitness. “If that’s impossible, try to only sacrifice your sleep two to three days during the week in order to hit the early morning cycling class. Get some extra sleep the other days and on the weekends.” That said, there are still a few hard and fast rules you can follow to determine what to do on those tough days when your bed feels oh-so-comfy.
If you got seven to eight hours of sleep the night before... You’re good to hit the gym, says Fable. Seven to nine hours of sleep is what most adults need, according to the National Sleep Foundation.
If you've been sleeping less than six hours most nights that week... It’s time to rethink your schedule, recommends Baron. See where you can cut corners to be more efficient: Head to bed 15 minutes earlier or shave 10 minutes off your morning routine to get a bit more sleep. If you're not a morning person, consider a lunch break or an after work gym time. (Try this Insanely Effective 15-Minute Workout when you’re crunched for time.)If you were up all night... Definitely skip the a.m. sweat sesh, says Fable. Not only do you need the sleep, but your coordination will be affected, making exercise potentially more dangerous. Your ratings of perceived exertion will also make exercise feel harder than it is, she warns. Even if you're working out at the same intensity as you usually do, sleep deprivation can mess with your mental performance, according to research in the journal Sports Medicine.
If you've only worked out once that week (and it's Friday)... If you're aiming for three to four workouts per week, it’s time to move, says Baron. Just 40 minutes of moderate to vigorous exercise three times per week can lower your risk for heart attack and stroke, says the American Heart Association. So don't hit snooze!
If you've been consistently killing it at the gym that week... Skip your workout, advises Fable. Everyone deserves a day off and your body needs sleep to repair after heavy workouts. Rest days allow for protein synthesis, which is crucial for building muscle, according to a study in the Journal of Strength and Conditioning Research.
If you're sore... Sleep in and take a day off. Overtraining can cause a decrease in sleep quality and duration, says Baron.