Soak Up the Benefits of Hot- and Cold-Water Immersion

You probably think of a hot bath as a way to unwind after an intense day — and a cold one as a way to wake up. But what if a soak could also boost your performance, not just in tomorrow’s workout, but potentially in all the ones after that?

In a recent study, exercise and sport-science professor Lance Dalleck, PhD, and his team at the High Altitude Performance Lab at Western Colorado University had athletes sit up to the neck in 102-degree water for 30 minutes immediately following a training session three times a week. (For reference, the average home bath should reach about 120 to 140 degrees if you turn the knob all the way to the left.) At the end of three weeks, the subjects showed a 3.2 percent improvement in their VO2 max (how efficiently your body uses oxygen), a 5.4 percent improvement in lactate threshold levels (which affect how long you can maintain higher intensity efforts), and a two- to three-fold improvement in running economy (how much oxygen your body needs to perform a given workout) compared to the control group.

To put a 3.2 percent improvement in VO2 max in perspective, Dalleck says that for someone who completes a 5-mile race in 40 minutes, it’d be equivalent to shaving 75 seconds off their time. The savings could be even more significant for someone who runs a slower pace.

Heat increases your blood plasma volume, says Dalleck, which allows your heart to more efficiently get more blood — and with it, more oxygen and fiber-repairing nutrients — to your working muscles. Heat also kick-starts the production of heat shock proteins that ultimately can allow for increased blood flow through your capillaries and help remove lactate and acid buildup caused by high-intensity exercise. “That can lead to a more rapid recovery,” says Dalleck. Other research shows that hot-water immersion can relax muscles and soften the collagen in your ligaments, which can help provide pain relief.

To soak up the perks, Dalleck recommends doing what his athletes did: sitting in your tub for half-hour sessions three times a week after moderate-intensity workouts. (P.S. One review found it takes at least six to seven baths to notice a difference.) But do it only after moderate-intensity workouts. “You want to elevate your core temperature to about 102 degrees, the sweet spot to bring about those adaptations that boost performance,” explains Dalleck. If you were to dip into a hot tub right after an intense session, your core temp might already be so high from working so hard that the hot water could put you at risk of heat illness.

What if you’re getting after high-intensity workouts and want some immediate relief? You might want to flip the faucet and follow in the footsteps of LA Laker LeBron James and Portuguese footballer Cristiano Ronaldo, who’ve posted images of themselves sitting in ice baths. Dalleck says that this method, called cold-water immersion, could help on occasions when you know you’re going to be sore and want cool relief (say, right after your first boot camp class in a long while). Just be forewarned that after certain workouts, ice baths may do more harm than good, he adds. A recent, albeit small, study published in the “Journal of Applied Physiology” found that cold-water immersion following resistance training could actually inhibit muscle growth.

If you do opt for an ice bath, the best protocol might be 11 to 15 minutes at a temp between 52 and 59 degrees, according to one review. The theory is that, like ibuprofen, the frosty water reduces soreness by blocking the inflammatory process caused by exercise. Some research suggests that cold water can reduce pain for up to four days post-exercise.

Of course, no one can argue that an ice bath is relaxing. But it might still offer a chance to hone your mindset and find some peace. Take it from Josh Bridges, a professional athlete and former U.S. Navy SEAL, who likens it to meditation. “Every morning I wake up and go straight to this cold tub set up outside my house. It literally sits at probably 34 degrees. I have to break the ice on the top layer, and then I get into it for four minutes of breathing,” he says. “If I can do that, then the rest of the day is going to be a cakewalk.”