With heat waves blanketing the country (again), a tall, frosty smoothie and post-workout ice bath probably sound appealing. But you might actually benefit more from a different—very different—recovery method, one that packs a three-for-one punch.
Hot water immersion—not cold—may improve recovery following exercise-induced muscle damage, according to a July 2024 study published in the journal Medicine & Science in Sports & Exercise. This joins a growing body of evidence that the benefits of heat therapy include better recovery, performance, and acclimation to rising temps.
Hot water for recovery
In the study, 30 physically active males immersed themselves in cold water (51°F) or hot water (105.8°F). Hot water immersion significantly improved the late-phase rate of force development, a measurement of explosive strength, and reduced muscle soreness. Cold water immersion was less effective in restoring explosive strength and managing soreness.
When you submerge your body in hot water, “the body will activate mechanisms to cool itself, including increasing blood flow to the skin surface to release heat,” explains Micah Zuhl, PhD, a professor at the School of Health Sciences at Central Michigan University. “To do this, the body dilates vessels to the skin and likely increases heart rate to help pump blood through those dilated vessels.”
That heat stress increases your blood plasma volume, explains Kevin Vincent, PhD, MD, head of the Sports Performance Center at the University of Florida and UF Health. “When you expand blood plasma volume, you get better delivery of oxygen and nutrients to your muscles and remove more lactic acid and other waste from those muscles.”
Heat also kick-starts the production of heat shock proteins, which help remove free radicals—or unstable molecules—that can cause cellular damage. “Repetitive heat exposure increases heat-shock protein levels, and higher levels mean more protection against heat and other stressors, such as exhaustive exercise and the oxidative stress that often accompanies aerobic exercise,” explains Dr. Zuhl. Both of those adaptations could help you recover faster.
At the same time, hot water “raises your body temperature, increases blood flow, and makes your tissues more elastic so you can get all your motor unity pliable and ready to generate more force,” adds Dr. Vincent.
“Heat makes your muscles feel better and more relaxed, so the pain decreases.”—Kevin Vincent, PhD, MD
There’s also a mind-body component to heat. “When you’re sore, you have lower force production,” says Dr. Vincent. “It’s not that your muscle fibers are so torn that they can’t produce force, it’s that the muscle is angry and sending a message to your brain that says ‘I’m hurt,’ which shuts off muscle activity to protect that body part. Heat makes your muscles feel better and more relaxed, so the pain decreases—it’s shutting that pain signal down and breaking that neurogenic inhibition.”
Heat for performance
Heat, research shows, can be a powerful recovery tool and a way to increase your performance—and it feels better than shivering through an ice bath. When people followed their workout with 30 minutes in water heated to 104°F, hot water immersion not only enhanced vascular and blood marker responses, it was more enjoyable than exercise alone, a study published in March 2024 in the Scandinavian Journal of Medicine & Science in Sports determined.
You don’t even need water. Post-exercise sauna bathing on average improved VO2 max—a measure of how efficiently your body can deliver oxygen to your muscles as you run—by around 8 percent, running speed by around 4 percent, and time to exhaustion by around 12 percent, according to a 2020 study published in the European Journal of Applied Physiology.
Translation: “At the end of a three-week period, people’s aerobic endurance and output was better because of that post-exercise sauna,” explains Dr. Vincent.
Heat acclimation in a warming world
Another benefit of heat therapy? It can be especially useful in preparing for more extreme conditions. Summer weather could last half a year by the end of this century, a 2021 warning in Geophysical Research Letters declared—in the last week of June alone this year, 1,400 heat records were broken across five continents, according to the Washington Post. And 75 percent of athletes across the globe who record their activities on Strava said extreme heat has affected their exercise plans, according to the fitness tracking app’s 2023 Year in Sports trend report.
“It should not be underestimated how much heat training helps,” says Dr. Vincent. “To get yourself acclimated to heat, you need to expose yourself to a hot environment.” The 2020 sauna study also declared post-exercise sauna bathing to be an alternative to active heat acclimation.
Heat acclimation is going to be essential for exercise moving forward.“To get your body ready for what it’s going to experience makes sense,” says Dr. Vincent. “Whether you’re improving your performance or not, you’re also reducing the risk of experiencing heat illness—which can be catastrophic.”
How to use heat smartly
But heat is a stressor, just like exercise is a stressor, so it should be deployed strategically as a training tool. You don’t want to use it after a high-intensity workout, when your core temperature is already significantly elevated. Instead, save it for immediately after moderate-intensity workouts—when you’re warm, but not overheated, says Dr. Zuhl. Three times a week is enough to bring out those positive adaptations.
Next time you’re looking to boost your recovery, don’t look any further than your own bathroom. A good post-workout soak will not only help you get back on your A-game faster, it can increase your fitness and help you better handle the conditions outside.
