There was a time, not long ago, when ice baths were de rigeur for serious runners. Collegiate runners retired to tubs of ice water after every workout, trying to avoid shivering because everyone knew that immersing your legs in cold water was the fastest way to recover for the next workout.

Over the years, protocols shifted from the hypothermia-inducing to the merely cold, as scientists and coaches realized that using water that’s too cold is simply an exercise in masochism.

But the cold-water bath remained a hallmark of the serious runner. I myself remember standing hip deep in the Pacific Ocean as the waves lapped over my legs and every fiber of my being wanted to flee. But of course, I didn’t. Because cold water after a tough workout was supposed to be good for you.

It turns out that maybe it isn’t.

One Chilled Leg

In a paper published December 1 in the online edition of The Journal of Physiology, a team of Dutch researchers tested cold-water baths in a dozen college-aged men undergoing a short (two-week) lower-body weightlifting program.

After each workout, the research subjects immersed one leg in cold water (46 °F) for twenty minutes. The other leg wasn’t chilled.

After the first session, they were also given a protein/carbohydrate recovery drink containing amino acids labeled with carbon-13, a non-radioactive isotope of carbon that provided a tracer for how well their muscles absorbed the drink’s amino acids.

And throughout the protocol, the researchers gave their subjects daily doses of “heavy water,” a form of water containing deuterium—a rare but also non-radioactive isotope of hydrogen. Because water (heavy or otherwise) is used by our bodies to produce amino acids, comparing how much of the deuterated water wound up in the proteins of the cold-water-treated leg muscles to the amount in their untreated leg muscles was a way of comparing overall protein synthesis in each leg.

The researchers then biopsied the study volunteers’ leg muscles several times, at various stages in the two-week experiment.

The first thing they found was that 20-25 percent less of the carbon-13 labeled amino acids were taken up by the muscles of the cold-water-bath legs than by the unchilled ones.

That’s significant because amino acids are the building blocks of proteins, necessary for muscle strengthening and repair.

Less Capable of Protein Synthesis

“We wanted to see if the process is affected by cold-water immersion,” says Cas Fuchs, a Ph.D. student at Maastricht University, Maastricht, Netherlands who is first author on the study. “We [found] that the cooled leg was less capable of muscle-protein synthesis.”

His team also found that at the end of two weeks of training, the cold-treated legs had built 11 percent less new protein than the untreated ones.

“This is important,” says Jonathan Peake, a sports scientist at Queensland University of Technology, Brisbane, who was one of the peer reviewers on the study. Peake notes that the new studies added to an increasing line of research on the negative effects of ice baths.

Reduced Strength and Endurance Gains

Previous studies had shown that ice baths may have deleterious effects on overall strength gain.

As far back as 2005, a team of Japanese researchers led by Motoi Yamane of Chukyo University did a study in which a dozen college-aged men were put on exercise bicycles for four to six weeks of training, immersing one limb, but not the other, in an ice bath (at temperatures ranging from 41 °F to 50 °F) after each session.

At the end of the training, Yamane’s team discovered that the non-ice-bathed limbs had gained more strength and endurance than the cold-water-treated legs—and that even the unchilled legs’ VO2 max (as measured in single-limb tests) had risen more than that of the ice-bathed legs.

More recent studies, Peake says, including some from his own research group, had also indicated that cold-water baths reduced the activity of cells and proteins that regulate muscle growth after exercise.

“But a question that remained unanswered was whether these responses translated to changes in muscle protein synthesis,” Peake says.  The new study, he says, adds to the case against ice baths by demonstrating “quite emphatically” that one of the ways this may happen is, indeed, by suppressing the rate of muscle protein synthesis.

Injury vs. Recovery

There are a few caveats, however.

First, this doesn’t answer if ice baths are good for injuries such as sprained ankles, where reducing swelling and pain is often a primary goal. “Injuries and exercise recovery are very different things,” Fuchs says.

Cold-water-bath enthusiasts can also argue about study protocols. It’s possible that the temperature in Fuchs’s study was too cold, or the immersion time too long. Not to mention that all of the study subjects were male, leaving it possible that women’s bodies might react differently. Nor was the study specifically focused on running.

Bottom Line: Ice Baths Reduce Recovery

But Fuchs thinks that the most likely explanation for his findings is one that probably applies across a broad spectrum of conditions. Most likely, he says, protein synthesis is impeded by the double whammy of chilling the muscle cells and reducing the blood flow to them—something that should be relevant to any sport, as well as to both men and women.

“With a reduction in muscle temperature, you slow down the processes within the muscle that are necessary to generate new proteins,” Fuchs says. “By reducing blood flow, you reduce the amount of building blocks (amino acids), that can be transported to the muscle… Everyone wants to get the most out of their workouts, [but] our research suggests that if the primary aim is to repair and/or build muscle, athletes should not use ice baths.”