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According to racehorses
Regular Exercise Helps Protect Muscles In Elderly
From Soreness, Injury
March 23, 2005 - Researchers now have the physical
evidence to show why it's important for older people to exercise. And it
comes with the discovery that, in aging racehorses, regular aerobic
workouts decreased the prevalence of muscle damage that can be caused by
exertion.
Mammalian skeletal muscle tissue is the same
regardless of which species of mammal it is in, said
Steven Devor, the study's lead author and an assistant professor of
exercise science education at Ohio State University.
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"We have to work at keeping muscle mass
as we age, otherwise that mass wastes away," Devor said. "This
weakness leaves a muscle more prone to injury even when it's the
least bit exerted. Also, joints are less likely to break if the
musculature surrounding them is strong."
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He and his colleagues studied the effects of
aerobic exercise in this case, galloping on a treadmill on small
sections of skeletal muscle tissue taken from the limbs of retired
racehorses. The findings support a use-it-or-lose-it philosophy: After
10 weeks of regular workouts, the horses' muscles showed fewer signs of
damage caused by exertion, even after the horses worked out at their
maximum capacity.
The results apply to humans and are especially
important for older adults, Devor said.
"We have to work at keeping muscle mass as we age,
otherwise that mass wastes away," he said. "This weakness leaves a
muscle more prone to injury even when it's the least bit exerted. Also,
joints are less likely to break if the musculature surrounding them is
strong."
"According to these results, aerobic exercise
training improves the ability of aging skeletal tissue to resist
injury," Devor said.
He and his colleagues report their findings in a
recent issue of the
Journal of Applied Physiology.
Some minor muscle damage is normal after a new or a
particularly difficult workout. The pain that often appears a day or two
after such exertion is called delayed onset muscle soreness, or DOMS.
"The way to get rid of this kind of pain is to stay
physically active," Devor said. "It's ironic, but muscles are most often
injured during exercise. But muscles get stronger by repairing this
damage."
The current study builds on experiments Devor
previously conducted in rats about 10 years ago, he helped identify
the mechanism that causes DOMS.
He was part of a team that found that this damage
happens when tiny skeletal muscle segments called sarcomeres the
smallest units of contractile muscle pull apart as a muscle lengthens.
Contractions that lengthen muscles are particularly
damaging to sarcomeres. And lengthening contractions are some of the
most common type of contractions humans do leg muscles contract and
lengthen as we sit down or walk and run, and arm muscles contract and
lengthen when we lower heavy objects.
The six quarter horses in the current study ranged
in age from 23 to 30 years, which made the animals elderly by horse
standards. A horse usually lives for about 28 to 32 years. The animals
used a treadmill a long conveyor belt built into the floor of a barn
three times a week for 10 weeks. Each workout lasted about 20 minutes.
The horses got little to no exercise during the three months leading up
to the study that way, the animals would have nearly the same fitness
level once the study began.
The researchers increased the speed and resistance
of the treadmill during each session, and the animals spent about 15
minutes of each workout exercising at a relatively high intensity.
Training protocols were updated every two weeks, based on the animal's
performance and its response to the given workload.
The researchers examined muscle tissue taken from
each horse's forelimb (triceps brachii) and hindlimb (semimembranosus
a large muscle of the thigh, and also the largest muscle the researchers
looked at.) Both muscles are used during walking and galloping. The
researchers also removed a small piece of the masseter, a muscle that
helps the jaw close during chewing. The masseter served as the control.
The researchers removed small portions of tissue
from each muscle before and immediately after the first and last
treadmill sessions, and also before and after a session during the
eighth week of training.
The treadmill was set at the same speed and
resistance during that eighth-week workout as it was during the very
first workout, in spite of increases in speed and resistance in the
weeks between the two sessions. The researchers wanted to see if nearly
two months of exercising would better protect the muscles from damage.
During the very last workout, the horses ran at their maximum capacity
until they reached exhaustion.
Eight weeks of exercise had a considerable effect
on the hindlimb muscle, as the degree of muscle damage had decreased
three-fold by then. After the first workout, the researchers noted a
five-fold increase in damaged sarcomeres compared to the muscle tissue
they examined prior to the workout.
"It wasn't serious damage, but the horses probably
felt a little sore afterward," Devor said. "A human would definitely
notice some soreness if they hadn't been regularly exercising."
After the workout during week eight, researchers
measured only a two-fold increase in the prevalence of sarcomere damage
in the hindlimb muscle. They saw the same results two weeks later, after
the very last treadmill session.
"The muscle had become more resistant to injury by
week eight," Devor said. "And it was stronger, too, since the horses
worked as hard as they could during the very last treadmill session."
The triceps, however, showed about the same amount
of sarcomere damage about two-and-a-half times more damage before
and after each of the workouts.
"The bigger muscle responded in a positive way to
several weeks' worth of conditioning," Devor said. "It suggests that the
protective effect of aerobic training may benefit larger muscles more
than smaller ones.
"It also suggests that there was less post-exercise
pain after the later workouts," he said, adding that the horses could
run up to 24 percent longer by the end of the study.
As expected, the masseter, or jaw muscle, was
unaffected by the workouts.
"The bottom line is that since the horses had kept
up with their training program, there were dramatic reductions in the
amount of muscle tissue injuries the animals had by the end of the
study," Devor said.
"This suggests that, in older adults, regular
exercise may help prevent injuries associated with age-related
impairments such as reduced muscle strength, impaired mobility and a
tendency to fall."
Devor conducted the study with Ohio State
colleagues Kenneth Hinchcliff, Mamoru Yamaguchi and Laurie Beard, all
with the college of veterinary medicine, and Chad Markert, formerly with
Ohio State's sport and exercise science program. The work was a portion
of the doctoral dissertation of Jeong-su Kim, who is presently at the
University of Alabama, Birmingham.
The study was supported by the Equine Research Fund
from the
College of Veterinary Medicine's Council for Research at Ohio State.
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