Because a lot of gyms have saunas in or attached to their locker rooms, it may seem like they're meant to go hand-in-hand with hard workouts. And the idea of relaxing in a hot room—whether it's a dry-heat sauna or a humid steam room—may be appealing, especially if you're feeling stiff or sore. But before you pair the two activities, there are a few precautions to keep in mind.
First, let's admit that sitting in a sauna does feel good. "It causes you to sweat and can help release endorphins," says David Geier, MD, a sports medicine specialist in Charleston, South Carolina. "And the heat also increases blood flow to the muscle and the periphery of the body, which probably does help sore muscles feel better temporarily."
But that doesn't necessarily mean using a sauna will help your workout recovery. "There's very little scientific evidence on sauna use for muscle soreness, especially the significant form of delayed onset muscle soreness—DOMS—that occurs 24 to 72 hours after exercise," says Geier.
That may be because DOMS is difficult to study in general; there's really not much evidence to definitively support any form of treatment—including commonly used ones like ice, massage, stretching, or anti-inflammatories.
"Honestly I think the sauna probably falls into the same category," says Geier. "It's probably not harmful and it may make you feel a little bit better during or immediately after, but it's unlikely that it will significantly decrease the intensity or duration of muscle soreness the next day."
Physical therapist Patrick Walsh, owner of Shift Integrative Medicine in New York City, notes that for temporary relief of sports-induced muscle soreness, using cold—like an ice pack—is generally more effective than using heat, which is usually reserved for treating older injuries or chronic muscle or joint pain, like arthritis.
Walsh wouldn't recommend using the sauna after a hard workout, either. "When you recover from exercise, your heart rate should come back down to normal," he says. "Sitting in a sauna for more than five minutes is going to keep your heart rate up—it's essentially a form of passive exercise—so it's really going to delay your body from starting its recovery process."
Spending a few minutes in the sauna before your workout is a better idea, he says, and may indeed help you feel warmed up and relieve some immediate muscle pain.
Both Walsh and Geier say the most important thing to keep in mind is replenishing your fluids—by some estimates, you'll lose a pint of sweat during just 15 to 20 minutes in a dry sauna.
"People ought to be careful how long they stay in, and make sure they drink enough water," says Geier. "You could easily get dehydrated, which can lead to more muscle soreness and lots of other complications." (And despite the fact that a recent study linked sauna use with reduced cardiac death, Geier still recommends that anyone with high blood pressure or a heart condition talk to their doctor before indulging.)
Bottom line: The sauna may help you feel better temporarily, and there's nothing wrong with using it separately from your workouts. But it may be best to avoid to the sauna after a hard workout. Make sure to drink plenty of water, and don't expect your sweat sessions to have much effect on muscle recovery in the long run.