What kind of heat is best?
There are many different ways to warm up your muscles: saunas, hot tubs, electric or chemical heating pads, wet towels, a cat that refuses to get off your chest. Which ones should you use and when?
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Several small studies have suggested that heat coming from a wet source, like a hot water bottle or moist towel, can be more effective than dry heat for preventing pain and reducing muscle damage from exercise. One study, conducted on participants who did a series of squats designed to make their quadriceps sore, suggested that moist heat penetrates deeper into tissue faster and works more quickly than dry heat.
However, most studies in this area have focused on small heating sources, like heating pads or wraps. It’s not clear whether full-body heat immersion, like using a hot tub or sauna, has the same effect on muscles as localised heat applied directly to an area.
Theoretically, immersion should have a similar effect, Chen says, on a larger scale. Rather than simply increasing blood flow to a small area, a hot tub or sauna speeds up circulation throughout your body and directs blood flow away from your muscles and towards your skin.
But most of the relevant research has focused on how regular immersive heat, such as a sauna several times a week, might improve health over time, rather than how a single session after a hard tennis game might make you feel.
What about temperature and timing?
To trigger many of the benefits of heat therapy, West says, “it has to be fairly hot to see some of these responses”.
Studies in animals have suggested that heat can have completely different effects depending on the exact temperature.
Most hot tubs are built to top out at 40 degrees to avoid heat stroke, says Chen. Local heat is less likely to give you heat stroke than immersive heat, but you should still be careful that your water bottle or heating pad is not so hot that it can burn you (which can happen if your skin reaches about 43 degrees).
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“That is something that actually happens more than you would think,” West says.
The best time to use heat on sore muscles seems to be immediately after exercise, and ideally for several hours. In a study in which participants wore out their leg muscles with squats, researchers compared the effects of using heat wraps right after exercising or 24 hours later. Muscles that were warmed immediately – for two hours with moist heat or eight hours with dry heat – experienced less damage and retained more strength than those heated later.
At the end of the day, there’s good reason to use heat on your muscles after a workout. “Physical therapists use a lot of heat,” says West. “Athletic trainers use a lot of heat.”
To give it a try on your own, she says, follow a few simple rules. First, pay attention to signs of dizziness that mean it’s time to get out of the sauna or hot tub. Second, don’t let a heating pad get so hot that you feel pain. Lastly, try to use it for several hours, but avoid falling asleep with it because the longer you keep it on, the more likely your skin is to burn.
The New York Times
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