Hydrotherapy is said to soothe sore muscles, but too-cold temps may compromise muscle strength and active recovery

By Rachael Schultz
July 22, 2015
Corbis Images

Post-race ice baths seem to be the new stretching-skip a cold soak after a race and you'll be sore and sorry tomorrow. And as this form of hydrotherapy, technically known as cold water immersion (CWI), has been studied more and more, we've become pretty darn convinced that ice baths post-workout work: They may indeed help decrease muscle soreness and speed recovery. But a new study in The Journal of Physiology suggests that while you may be less sore in the days to come, ice baths on the reg may actually compromise how much muscle you'll end up building from your workouts.

The Study

Australian researchers conducted two experiments, publishing their findings online last week. They found that chilly post-workout soaks may actually endanger the muscle growth and strength you're supposed to gain from your time spent at the gym.

In the first study, the scientists had 21 people strength train twice a week for 12 weeks. Half of the participants followed up the workout with a 10-minute ice bath; the other half did 10 minutes of easy stationary cycling. After three months, the ice bath group had less muscle mass and weaker strength on a leg press than the group that had been following an active recovery. For what it's worth, both groups saw muscle growth (probably thanks to the workout, not the recovery method)-the ice bath group just didn't have as much.

To dig even deeper, the researchers conducted a similar but far more specific experiment: Nine of the participants performed two strength workouts, one followed by CWI and the other followed by active recovery. Researchers biopsied their muscles before and after both workouts and found that after the ice bath, the cellular signaling that helps muscles develop decreased. Why that's worrisome: Cellular signaling communicates what are called muscle adaptation signals, which help regulate carbohydrate and fat metabolism in response to your muscles' needs. If this signaling is inhibited, your muscles aren't being fed the proper nutrients to help them build. Over time, this can compromise muscle gain and strength-results that held from the first study.

So what gives? Why could ice baths do such terrible things?!

The Argument

Well, don't blame the baths quite yet. Since researchers were looking specifically at the effects of cold water, other important factors in muscle-building were left uncontrolled, so it's difficult to say all potential strength lost was due to CWI. "Post-exercise nutrition and sleep are of the utmost importance for active muscle growth," says Harry Pino, Ph.D., exercise physiologist at the Sports Performance Center at NYU Langone Medical Center. (And these 7 Nutrients Help Increase Muscle Tone.)

Even more: Researchers only looked at the effects of CWI on strength athletes and, therefore, effects relating to fast-twitch muscle fibers, Pino points out. These fibers are the kind responsible for your ability to endure high-intensity activities, but there's another type of fiber too-slow-twitch, which help your muscles last longer in events like endurance races. And the two react differently to external factors (think: everything from the intensity and duration of your workout to the temperature of your recovery).

What we do know: A study published just last month in the American Journal of Physiology found that cold water immersion can actually be beneficial for helping muscle grow, as it can boost the formation of new mitochondria, the powerhouses of your muscle cells that help you move faster and give you power, Pino says. (Since exercise damages your muscles, it breaks down the mitochondria.) The formation of new mitochondria is especially important in endurance training for stamina, but also in strength training for explosiveness. Adding new mitochondria means fibers get thicker and your muscles appear bigger, Pino explains.

Ultimately, though, the effect of cold water immersion on muscle growth may be somewhat of a moot point: The main reason athletes turn to cooling is to speed muscle recovery-something which is pretty well supported by scientific and anecdotal evidence, Pino says. Cold water constricts blood vessels, helping to flush by-products (like lactic acid) out of your lymph nodes and lower inflammation, both of which help reduce muscle soreness. (Other great alternatives: The Best Ways to Ease Sore Muscles.)

The Verdict

So should you slide into the cold? If your focus is on reducing soreness, it may help. However, Pino actually recommends CWI just for recovery after high-intensity workouts. After sprints or high-intensity strength training, you can nix next-day soreness by dipping into a 50-degree bath for eight to 10 minutes. What he has found in his own athletes (and which a growing body of research supports) is that compression garments and a lot of active stretching are the best ways to recovery after low-intensity exercise (like long runs below 70 percent of your max).

In all likelihood, you'll still see a gain in muscle size and strength from all the sweaty hours you've been logging, plus your next-day soreness will settle down faster. And that's the cold, hard truth.