Regular aerobic exercise in horses and people

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Source: Ohio State University

Date: 2005-03-25

URL: http://www.sciencedaily.com/releases/2005/03/050323151009.htm

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Regular Exercise Helps Protect Muscles In Elderly From Soreness, Injury

COLUMBUS, Ohio - 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 Devor, the study's lead author and an assistant

professor of exercise science education at Ohio State University.

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 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.

Editor's Note: The original news release can be found here.

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This story has been adapted from a news release issued by Ohio State

University.