After a particularly vigorous workout or sports injury, many of us rely on ice packs to reduce soreness and swelling in our twanging muscles. But a cautionary new animal study finds that icing alters the molecular environment inside injured muscles in detrimental ways, slowing healing. The study involved mice, not people, but adds to mounting evidence that icing muscles after strenuous exercise is not just ineffective; it could be counter-productive.
Check inside the freezers or coolers at most gyms, locker rooms or athletes' kitchens and you will find ice packs. Nearly as common as water bottles, they are routinely strapped onto aching limbs after gruelling exercise or possible injuries. The rationale for the chilling is obvious. Ice numbs the affected area, dulling pain, and keeps swelling and inflammation at bay, which many athletes believe helps their aching muscles heal more rapidly.
But, in recent years, exercise scientists have started throwing cold water on the supposed benefits of icing. In a 2011 study, for example, people who iced a torn calf muscle felt just as much leg pain later as those who left their sore leg alone, and they were unable to return to work or other activities any sooner. Similarly, a 2012 scientific review concluded that athletes who iced sore muscles after strenuous exercise — or, for the masochistically minded, immersed themselves in ice baths — regained muscular strength and power more slowly than their unchilled teammates. And a sobering 2015 study of weight training found that men who regularly applied ice packs after workouts developed less muscular strength, size and endurance than those who recovered without ice.
But little has been known about how icing really affects sore, damaged muscles at a microscopic level. What happens deep within those tissues when we ice them, and how do any molecular changes there affect and possibly impede the muscles' recovery?
So, for the new study, which was published in March in the Journal of Applied Physiology, researchers at Kobe University in Japan and other institutions, who long had been interested in muscle physiology, gathered 40 young, healthy, male mice. Then, using electrical stimulation of the animals' lower legs to contract their calf muscles repeatedly, they simulated, in effect, a prolonged, exhausting and ultimately muscle-ripping leg day at the gym.