Blasts of super cold air may feel good on overworked muscles, but the increasingly popular form of cryotherapy does not stop muscle soreness or declines in muscle strength, according to a new study.
Though other measures of muscle injury, such as swelling and muscle-cell electrical activity, were slightly improved after the rapid cooling, "overall, it's ineffective," said Gaël Guilhem, the lead author of the study and a researcher at the National Institute for Sports in Paris, France.
What athletes are interested in, Guilhem said, is, "'am I (in less pain), am I stronger?' And the answer was, 'no.'"
Ice has long been used as a therapy for muscle injury.
"It's been the standard treatment for acute injury and chronic injury since the 70s," said Ty Hopkins, a professor at Brigham Young University, who was not part of the study.
Since then, approaches to cooling damaged tissues have become more sophisticated, involving machines that can use pulses of extremely cold air to quickly cool down sites of injury without hurting the skin.
Hopkins said such techniques have been gaining popularity recently in the context of attempts to reduce muscle damage after exercise.
Working muscles hard causes tiny tears in the fibers - whose repair ultimately makes muscles grow larger. But in the wake of the immediate injury, the muscle gets weak, inflamed and painful.
Although icing muscles can act as a painkiller, studies have not always agreed on whether the practice can prevent damage to the muscle tissue.
Guilhem and his colleagues asked 24 men to induce a muscle injury in their arm. The volunteers repeatedly unfolded one arm until it was straight while pushing against a resistance machine.
Within a day the muscles in each man's exercised arm were sore, and the researchers tracked their status for two weeks.
Half of the men received cryotherapy right after the strenuous exercise and again at one, two and three days later, while the other half received no extra intervention.
The therapy involved three applications, each lasting four minutes, of air cooled down to -30 degrees Celsius (-22 Fahrenheit).
Muscle strength in both groups dropped a day after the exercise, but the cooling therapy offered no benefit to those who received it, the researchers report in The American Journal of Sports Medicine.
Muscle soreness peaked a few days after the exercise and gradually declined over the next two weeks, but, again, having rapidly cooled the injured muscle made no difference in pain over the long term.
One of the measurements that did vary between the groups was inflammation, as marked by a protein in the blood called C-reactive protein.
The protein remained steady among the men who received the cryotherapy, while those who received no intervention had a 93 percent increase in C-reactive protein three days after the muscle exercise.
Guilhem and his colleagues also used electromyography - a large electrode on the muscles - to observe muscle "activity" during an exercise, a measure of the extent of muscle injury.
"What we saw is that the cryotherapy group preserved their muscle activity for around two days," Guilhem told Reuters Health.
In other words, while both groups developed declines in muscle activity, the cryotherapy group maintained activity for longer before that decline.
Guilhem added that the difference between the groups was very slight, however, "and it doesn't have an impact on muscle performance."
"It makes some sense that if you cool a damaged muscle, the muscle is not necessarily going to act differently because the muscle itself is damaged," he told Reuters Health.
While cryotherapy might not have a great effect in the context of a strenuous workout, that doesn't mean it won't have benefits in other situations, such as a joint injury, Hopkins said.
Guilhem said that cryotherapy could help people feel more comfortable while recovering from a muscle injury.
Hopkins agreed that cooling can be a helpful intervention in other ways.
"It works very well to limit secondary injuries, to limit swelling, to limit pain, and there's no downside to it," he told Reuters Health.
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