Feb. 2, 2000 Writer: Kristin Harmel
Source: Scott Powers, (352) 392-9575, firstname.lastname@example.org
GAINESVILLE, Fla. --- Heat therapy can reduce the amount of muscle lost during limb immobilization, according to a new study by researchers from the University of Florida and Juntendo University in Japan.
The study has broad implications for people who must have their limbs immobilized because of bone injury or during bed rest as well as for astronauts, whose muscles often atrophy in the weightlessness of space, said Scott Powers, a professor in UF's department of exercise and sport sciences.
"There are all kinds of conditions in which patients can't exercise," Powers said. "If people can lift weights, they can retard atrophy, but if a limb is broken or a person in bedridden, they obviously can't maintain muscle mass that way."
Muscle atrophy was 32 percent lower in rats that had been treated with heat therapy before the muscles were made inactive compared with muscles that were not treated but also were made inactive, according to the study, which appears in the current issue of the Journal of Applied Physiology.
Exercise physiology Professor Hisashi Naito from Juntendo University and UF Professor Stephen Dodd also participated in the study, which is the first to show that heat therapy provides protection against muscles atrophy in suspended limbs, Powers said. It likely will lead to future studies in which humans receive heat treatment.
Researchers divided 40 adult rats into four groups. The first group received no treatment; the second group was exposed for 15 minutes to temperatures of 106.9 degrees Fahrenheit; the rats in the third group had their hind limbs suspended and recived no heat treatment; and the rats in the fourth group were treated with heat at 106.9 degrees Fahrenheit and had the weight removed from their hind legs.
After eight days of hind limb suspension, which mimicked weightlessness and prevented muscle use, researchers measured the degree of muscle atrophy in a prominent leg muscle. They analyzed the muscles for protein content and for levels of the heat shock protein HSP72, a stress protein produced in the cells by excessive heat and known to protect cells from some types of damage. In rats that had been treated with heat, researchers found much higher levels of HSP72 and lower levels of muscle atrophy.
HSP72 levels in rats that received no heat therapy and had their hind legs suspended were 40 percent below normal, the study showed, while HSP72 levels in rats that received heat treatment and had their legs suspended were 35 percent above normal values.
"Muscle atrophy occurs when there is a decrease in the rate of protein synthesis and an increase in the rate of breakdown of protein in the muscles," Powers said. "If you're trying to develop a countermeasure that maintains muscle mass, it makes sense to try to maintain the rate of synthesis."
Powers believes elevated HSP72 levels counter the reduction in protein synthesis caused by muscle disuse.
Because HSP72 has a half-life of only seven days, heat would have to be reapplied approximately every week to maintain HSP72 levels in the muscle, Power said. However, raising the temperature of the body enough to promote HSP72 synthesis is a relatively easy process and in fact took only 15 minutes in the rats.
"I don't see why these kinds of tests couldn't begin very soon," Powers said. "It's a safe and non-invasive way to treat muscle loss."
The researchers currently are studying mechanisms that also would slow protein degradation in muscles. When used in conjunction with HSP72, the maintenance of muscle mass during immobilization might be even more successful, Powers said.
While the study's most common application might be to average patients who have broken a bone, its most important application might be to older people, whose bone injuries often take longer to heal and whose levels of muscle mass already are depleted.
"If an 80-year-old breaks a hip and goes to bed for six to eight weeks, he or she may never be able to walk again," Powers said. "This may have particular relevance to an aging population, because maintaining muscle mass and strength has a lot to do with the quality of life."
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