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
counterproductive.
اضافة اعلان
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 grueling
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.
Rodents’ muscles, like ours, are made up of fibers that
stretch and contract with any movement. Overload those fibers during unfamiliar
or exceptionally strenuous activities and you damage them. After healing, the
affected muscles and their fibers should grow stronger and better able to
withstand those same forces the next time you work out.
But it was the healing process itself that interested the
researchers now, and whether icing would change it. So they gathered muscle
samples from some animals immediately after their simulated exertions and then
strapped tiny ice packs onto the legs of about half of the mice, while leaving
the rest unchilled. The scientists continued to collect muscle samples from
members of both groups of mice every few hours and then days after their
pseudo-workout, for the next two weeks.
Then they microscopically scrutinized all of the tissues,
with a particular focus on what might be going on with inflammatory cells. As
most of us know, inflammation is the body’s first response to any infection or
injury, with pro-inflammatory immune cells rushing to the afflicted area, where
they fight off invading germs or mop up damaged bits of tissue and cellular
debris. Anti-inflammatory cells then move in, quieting the inflammatory
ruction, and encouraging healthy new tissue to form. But inflammation is often
accompanied by pain and swelling, which many people understandably dislike and
use ice to dampen.
Looking at the mouse leg muscles, the researchers saw clear
evidence of damage to many of the muscles’ fibers. They also noted, in the
tissue that had not been iced, a rapid muster of pro-inflammatory cells. Within
hours, these cells began busily removing cellular debris, until, by the third
day after the contractions, most of the damaged fibers had been cleared away.
At that point, anti-inflammatory cells showed up, together with specialized
muscle cells that rebuild tissue, and by the end of two weeks, these muscles
appeared fully healed.
Not so in the iced muscles, where recovery seemed markedly
delayed. It took seven days in these tissues to reach the same levels of
pro-inflammatory cells as on day three in the unchilled muscle, with both the
clearance of debris and arrival of anti-inflammatory cells similarly slowed.
Even after two weeks, the iced muscles showed lingering molecular signs of
tissue damage and incomplete healing.
The upshot of this data is that “in our experimental
situation, icing retards healthy inflammatory responses,” said
Takamitsu Arakawa, a professor of medicine at Kobe University Graduate School of Health
Sciences, who oversaw the new study.
But, as Arakawa pointed out, the experimental model simulated
serious muscle damage, such as a strain or tear, and not simple soreness or
fatigue. The study also, obviously, involved mice, which are not people, even
if our muscles share a similar makeup. In future studies, Arakawa and his
colleagues plan to study gentler muscle damage in animals and people.
But for now, Arakawa said, his study’s findings suggest that
damaged, aching muscles know how to heal themselves, and our best response is
to chill out and leave the ice packs in the cooler.
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