Sports science, circa 2005, was pretty confident that ice baths accelerate recovery by fighting the inflammation in muscles after a hard workout. The actual evidence that ice baths really hastened recovery was admittedly ambiguous, but the idea that cold fights inflammation seemed self-evident.

By 2015, the message was less certain. Yes, ice baths fight inflammation, but they might actually fight it too well. Since post-workout inflammation is one of the signals that tells your muscles to repair, adapt, and get stronger, regular ice baths might actually reduce the fitness gains from training.

Now there’s another plot twist. A new study in the Journal of Physiology, by an international team led by Australian researcher Jonathan Peake of the Queensland University of Technology, suggests that ice baths don’t actually do anything to fight post-workout inflammation.

It’s worth taking a step back to point out that “inflammation” is not the same thing as “swelling.” Inflammation is the body’s response to certain harmful stimuli, characterized—as Aulus Cornelius Celsus’s De Medicina noted two thousand years ago—by “calor, dolor, rubor, tumor,” or heat, pain, redness, and swelling. It involves the activation of a huge variety of different cells and molecular signalers, and the ramping up of blood supply to the affected area, with the goal of fighting off pathogens or repairing tissue damage.

The study involved nine men who performed one-legged resistance exercise and then either took an ice bath (10 minutes at 10 degrees Celsius /50 degrees Fahrenheit) or did 10 minutes of easy cycling. On another day, they exercised the opposite leg and did the other post-workout routine. The researchers took a bunch of blood samples, plus muscle biopsies before, two hours after, 24 hours after, and 48 hours after the workout.

To assess the results, they tested a long list of “inflammatory cells, pro-inflammatory cytokines, neurotrophins and heat shock proteins.” I don’t have enough expertise in this area to say much about the relative significance of all these things—neutrophils, macrophases, TNF, IL6, and so on. But the bottom line is this: Exercise, as expected, increased the cellular signs of inflammation—but there was no difference between a post-workout ice bath and a 10 easy minutes on a bike.

At first glance, you might assume this means that the study is suggesting that ice baths don’t do anything. But that’s not necessarily the conclusion. In fact, the same researchers have previously shown that ice baths do trigger changes in parameters like blood flow in the affected muscles. Other researchers have shown that cold water can reduce swelling that results from edema, when excess fluid accumulates (as opposed to swelling associated with inflammation).

And these findings don’t change the fact that (a) many previous studies have found that ice baths do reduce perceptions of soreness and speed up the recovery of muscle function; and (b) some studies have, conversely, found that long-term use of ice baths interferes with training adaptations.

Instead, the results suggest that neither the positive nor the negative effects of ice baths are the result of reducing inflammation, or cellular stress in general, in the affected muscle. Perhaps it’s the reduction of blood flow to the muscles that matters; perhaps it’s the change in muscle temperature. Whatever the mechanism, it’s worth trying to figure it out—because that’s how we’ll figure out the best way to balance short-term recovery gains with long-term training adaptations.

For now, my practical advice remains pretty much the same. If you find that ice baths help, keep using them—but consider periodizing their use, so that you use them most when you’re approaching competition or need to recover rapidly. Use them more sparingly during periods of heavy training, when adaptation is the goal. If you don’t like ice baths, on other hand, I don’t see any compelling reason to start using them.

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