Opportunities to chill aching or injured body parts have moved beyond the ice-pack aisle. A trendy technique called cryotherapy offers whole-body immersion in chambers where the temperature can drop to 150 degrees below zero.
The website of a facility in Minneapolis, where I live, claims that the practice fights inflammation, reduces pain and soreness, and speeds healing, all for $35 a session or $450 for unlimited visits each month.
But does cooling weary muscles do any good — whether with a pack of frozen peas or a full-body immersion?
Although the idea that cold can heal is ancient, scientists have only recently begun to test the idea of treating swelling and pain with “RICE”: rest, ice, compression and elevation. And as data have accumulated, so too have doubts. So far, scientists have failed to find strong evidence that cold therapies can help with much of anything, including muscle soreness or recovery from exercise.
There may even be dangers, such as frostbite. Full-body cryotherapy might carry occupational hazards, too. In October, a worker at a spa in Nevada froze to death in a cryotherapy chamber that she had entered after hours. Details about what happened remain unclear.
A less dire but still important concern is that by interfering with the body’s inflammatory process, icing might actually slow healing.
“There’s more and more evidence coming out that the inflammation that cold reduces is actually imperative for the recovery and healing process,” says Joseph Costello, an exercise physiologist at the University of Portsmouth in the United Kingdom. “The human body is more intelligent than an ice pack.”
At least one thing is certain about icing: It lowers tissue temperatures. It also often dampens pain. A possible explanation for this analgesic effect is that cold slows the speed at which nerves fire while constricting arteries and veins and limiting blood flow, which reduces inflammation.
Less clear is whether cold can help in any measurable way. Many marathon runners swear by sitting in ice-cube-filled bathtubs after long runs, for instance. But a 2012 review of 17 trials found little evidence to support the practice, in part because the studies were small in size, low in quality and varied in protocols. Overall, the researchers concluded that cold-water immersion might help reduce the pain that occurs a day or two after hard exercise. But there wasn’t enough data to say anything about the effects of cold on such other factors as fatigue or recovery.
In another 2012 review of 35 studies that looked at sports performance, Irish researchers found a hodgepodge of conflicting results. Six of the studies showed that cooling led to a reduction in an athlete’s speed, power and running-based agility. But two studies found that a quick rewarming period nullified that effect. Most of the studies found that strength suffered immediately after cooling. But they also noted plenty of flaws across the studies, including their small size, with an average of just 19 participants in each trial.
Even though icing has long been standard practice among athletes at all levels, it doesn’t make a lot of sense physiologically, says Dain LaRoche, an exercise physiologist at the University of New Hampshire. A 2013 study that he co-authored found no difference in soreness or strength between runners who iced and didn’t ice after a workout, though it did find a slight drop in inflammation markers in those who used ice therapy. Another study looked at the effects of icing just one leg after a cycling exercise: It found that muscular benefits from the exercise were greater in the leg that didn’t get iced.
Those results suggest that icing dampens the body’s ability to repair and strengthen the tiny tears that happen in muscle tissues during intense exercise. “People who ice themselves after every run could be blocking inflammation that leads to adaptation,” LaRoche says. “There’s no evidence to support [icing] being beneficial, and it could, in fact, be detrimental.”
When cold therapies do seem to help, their effects might be based in the brain, not the muscles, some experts suspect, though research on that is also limited. For a 2014 study, Australian researchers put 30 young men through a high-intensity sprint workout to make them sore. Then they were assigned to spend 15 minutes in one of three bathtubs: One contained very cold water (about 50 degrees); another was filled with water warmed to body temperature (about 95 degrees); the third likewise had body-temperature water but it also contained soap that participants were told was beneficial for recovery from intense exercise. (In fact, it was just ordinary soap.)
Results showed equal benefits from both the cold bath and the “magic-soap” bath. In both conditions, participants reported less soreness than those who took a soap-free warm bath, and they performed better on a strength test.
This kind of placebo effect, Costello says, might also explain anecdotal reports raving about whole-body cryotherapy, despite a lack of evidence to support it. When he and colleagues searched for studies examining the extreme-cold treatment, they found just four lab-based, randomized controlled trials. All were plagued by familiar limitations, they reported in a review last year: Participants were mostly male, young and fit. Sample sizes were tiny. And study designs varied significantly.