Many of us rely on ice packs to reduce the pain and swelling of twisted muscles, especially after intense training and sports injuries. However, careful new animal studies have found that icing alters the molecular environment in damaged muscle in a detrimental way, delaying healing. Although the study targeted mice rather than humans, there is increasing evidence that muscle icing after strenuous exercise is not only ineffective. It can be counterproductive.
You can find ice packs by looking inside the freezer or cooler of most gyms, locker rooms, or athletes’ kitchens. Almost as common as a water bottle, but strapped to a daily aching limb when there is a risk of strenuous exercise or injury. The rationale for cooling is clear. Ice paralyzes the affected area, dulls pain, and reduces swelling and inflammation. Many athletes believe that painful muscles help heal faster.
But in recent years, exercise scientists have begun to throw cold water into the potential benefits of icing. For example, in a 2011 study, people with torn calf muscles felt as much pain in the lower limbs as those who left the pain in their legs and could not return to work or other activities immediately. Similarly, a 2012 scientific review found that athletes who had frozen muscle soreness after strenuous exercise, or who had a masochistic spirit, regained strength and power more slowly than their uncooled teammates. I conclude. And a cool study of weight training in 2015 found that men who regularly applied ice packs after training had less muscle strength, size, and endurance than men who recovered without ice.
However, little is known about how icing actually affects painful and injured muscles at a microscopic level. What happens deep inside those tissues when we freeze them, and how molecular changes there affect and perhaps prevent muscle recovery?
So, for a new study published in the Journal of Applied Physiology in March, researchers at Kobe University and other institutions in Japan have long been interested in muscle physiology, so 40 young and healthy animals. I collected a lot of male mice. Next, electrical stimulation of the animal’s lower limbs was used to repeatedly contract the calf muscles, effectively simulating a long, exhausted, and finally muscle-tearing leg day in the gym.
Rodent muscles, like us, are made up of fibers that stretch and contract with any movement. Overloading these fibers during unfamiliar or very intense activity can damage the fibers. After healing, the affected muscles and their fibers grow stronger and can withstand the same forces the next time you exercise.
But now researchers are interested in the healing process itself, and whether freezing will change it. There, they collected muscle samples from several animals immediately after the simulated exercise and strapped a small ice pack to about half the legs of the mouse without cooling the rest of the mouse. Scientists continued to collect muscle samples from mouse members in both groups for the next two weeks, every few hours, and days after simulated training.
Next, all tissues were examined under a microscope, with a particular focus on what was happening with the inflammatory cells. As most of us know, inflammation is the body’s first response to infections and injuries, where pro-inflammatory immune cells rush into the affected area, repelling invading bacteria and damaging tissues. Wipe off cell debris. The anti-inflammatory cells then move in, calming the inflammatory inflammation and promoting the formation of healthy new tissue. However, inflammation is often accompanied by pain and swelling. Many people hate it and moisten it with ice.
Looking at the leg muscles of mice, researchers saw clear evidence that many of the muscle fibers were damaged. They also noted the rapid convocation of pro-inflammatory cells in non-frozen tissues. Within hours, these cells began busy removing cell debris, and by the third day after contraction, most of the damaged fibers had been removed. At that point, anti-inflammatory cells appeared along with specialized muscle cells that restructured the tissue, and by the end of the two weeks these muscles appeared to be completely healed.
This is not the case with frozen muscles, where recovery appears to be significantly delayed. In these tissues, it took 7 days to reach the same level of pro-inflammatory cells as on day 3 of uncooled muscle, and both debris removal and anti-inflammatory cell arrival were similarly delayed. Even after two weeks, these muscles showed protracted molecular signs of tissue damage and incomplete healing.
The conclusion of this data is that “in our experimental situation, icing delays a healthy inflammatory response,” said Takamitsu Arakawa, a professor of medicine at the Graduate School of Health Sciences, Kobe University, who oversaw a new study.
However, as Dr. Arakawa points out, their experimental model simulates serious muscle damage such as tension and laceration, rather than simple pain and malaise. Obviously, this study targeted non-human mice, even though our muscles share a similar composition. In future studies, Dr. Arakawa and his colleagues plan to study milder muscle damage in animals and humans.
But so far, his findings suggest that damaged painful muscles know how to heal themselves, and our best bet is to chill and put the ice pack in a cooler box. It is to keep it.
Ice for muscle aches? Think again.
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