Cold-immersion therapy—colloquially known as cold therapy or ice baths—has long been a recovery method used by hardcore lifters, pro athletes, and ultramarathoners looking to initiate and enhance the healing process after a taxing training session. Trouble is, plunging neck-deep into a bone-chilling, testicle-shrinking tub of ice may not be so helpful.

 In a study published in the Journal of Physiology, researchers asked 21 physically active men to begin a strength-training regimen two days a week for 12 weeks. About half the group withstood a 10-minute post-workout ice bath at a numbing 50 degrees, while the rest sidestepped the soak and cooled down by pedaling on a stationary bike instead. After three months, those who performed an active cooldown on the bike experienced greater strength and muscle gains than those who braved repeated ice baths.
A follow-up study confirmed the findings. In this one, men performed single-leg strength exercises, then took an ice bath or cooled down on a bike. After researchers took and analyzed muscle biopsies, they found that the ice baths stunted activity in satellite cells—essentially muscle stem cells—and in pathways needed to build bigger, stronger muscles.
“We found that cold-water immersion after training substantially attenuated, or reduced, long-term gains in muscle mass and strength,” said Llion Roberts, Ph.D., the study’s lead author.

The researchers surmise that athletes who regularly take ice baths after lifting weights will see less muscle growth and strength improvements than those who choose active cooldowns (like hopping on a bike), because the frigid water reduces blood ow to the muscles.

BOTTOM LINE: Don’t go full Polar Bear Club after training. INSTEAD, WALK, RUN, OR CYCLE AT AN EASY PACE TO END YOUR WORKOUT— unless you want small, weak, half-frozen muscles.