Aerobic Exercise Helps Maintain Muscle In Elderly

[Guest guest]

Aerobic Exercise Helps Maintain Muscle In Elderly, Study Suggests

Science Daily — Why do older people tend to lose muscle mass and grow

frail? One important factor identified by medical science is the

reduced ability of the elderly to respond to the muscle-building

stimulus of the hormone insulin.

Insulin is best known for its link to diabetes -- a condition in which

either a complete lack of insulin or systemic resistance to the

hormone's activity (as in type 2 diabetes) causes blood sugar levels

to soar out of control. Recent studies have shown, however, that

insulin also provides crucial assistance in building muscle, and that

its ability to do so drops off dramatically in the elderly.

Now, a small but provocative study by medical researchers in Texas and

California suggests that a simple, cost-free therapy appears to

largely overcome that drop-off in insulin response: moderate aerobic

exercise such as walking.

Experiments at the University of Texas Medical Branch at Galveston

(UTMB) and the University of Southern California, Los Angeles

conducted on 13 healthy volunteers in their late 60s showed that 45

minutes of walking 20 hours before exposure to insulin restored the

muscle-growth-stimulating effects of the hormone to levels comparable

to those seen in normal young adults.

Prior research had suggested that a large part of the problem older

people experience lies in the tiny blood vessels that feed the muscles

protein-building amino acids, glucose and insulin (which itself also

works within muscle cells as a powerful protein growth factor). In

young adults, these normally closed vessels open wide in response to

the insulin increase generated by a meal, providing clear passage for

muscle-making materials. In elderly people, however, this process,

known as " vasodilation, " is much less pronounced.

" We thought, let's see what happens if we use aerobic exercise, one of

the interventions that has been shown in the past to improve

vasodilation, to find out whether we can get insulin to stimulate

muscle synthesis in older people, " said UTMB professor Elena Volpi,

senior author of a paper on the experiments appearing in the June

issue of the journal Diabetes. " It turned out that a fast walk

restored the insulin response quite well. "

To test their hypothesis, the researchers first required six of their

13 subjects to walk for 45 minutes on a treadmill quickly enough to

keep their hearts beating at 70 percent of their maximum rate --the

same aerobic intensity level recommended to maintain cardiovascular

fitness. The other seven subjects simply rested.

On the following morning, the researchers sampled the blood going into

and coming out of thigh muscle in each of the volunteers, while

supplying via the femoral artery a concentration of insulin similar to

that released after a typical meal. They also took three small muscle

tissue samples from each subject.

Tracer techniques enabled the scientists to track amino acids (the

building blocks of muscle proteins) and determine muscle-protein

synthesis and breakdown rates from the blood and muscle samples, while

measuring blood flow at the same time. These revealed that the

volunteers who exercised had both higher blood flow and net muscle

protein growth. In addition, the researchers screened the muscle

biopsy samples for signals associated with insulin's ability to

stimulate the assembly of muscle protein from amino acids. This test

also showed that exercise boosted insulin's role as a muscle protein

growth factor.

" We already know that moderate aerobic exercise reduces cardiovascular

disease, improves glucose uptake, and improves endurance, " Volpi said.

" Now it looks like it may also slow the rate of muscle loss in aging.

We need to test this hypothesis further with larger trials, but still,

it's one more reason why elderly people ought to be regularly walking,

swimming or cycling. "

Other authors of the Diabetes paper are UTMB postdoctoral fellows

Satoshi Fujita and Jerson Cadenas, associate professor Blake B.

Rasmussen, physical therapy graduate students Micah J. Drummond and

L. Glynn, and USC-Los Angeles professor Fred R. Sattler.

This research was supported by two grants from the National Institute

on Aging, including UTMB's Claude D. Pepper Older Americans

Independence Center; the E. and May R. Foundation; the

National Institute for Arthritis and Musculoskeletal and Skin

Diseases; and the NIH-funded General Clinical Research Centers at UTMB

and USC.

Note: This story has been adapted from a news release issued by

University of Texas Medical Branch at Galveston.