ATHENS, Ohio -- Older people who begin an exercise program following a period of inactivity may find that their muscle development isn't what it used to be. A new study at Ohio University suggests that changes in the muscle that occur during the aging process may control muscle growth in the elderly, limiting them to the same amount of muscle growth as young people who don't exercise.
Researchers studied groups of young and elderly men, some of whom participated in a 16-week exercise program. The findings suggest that the number of special cells required for muscle growth decreases as people age, making it more difficult to replace muscle nuclei lost because of atrophy induced by a lack of exercise.
"We're not sure whether an older person can maintain the muscle fiber size of a young person with continuous training, but it looks like the amount of muscle growth in older muscles is limited due to the changes that occur in the muscles with aging," said Robert Hikida, professor of anatomy in biological sciences and the College of Osteopathic Medicine at Ohio University and co-author of the study.
Hikida presented the information May 30 at the annual meeting of the American College of Sports Medicine in Denver.
Cells in skeletal muscles can contain hundreds of nuclei -- called myonuclei. Each controls a specific area of the muscle cell and contributes to the overall cell growth. Myonuclei are added to or replaced by special cells called satellite cells. A decrease in satellite cells appears to cause a decrease in the capacity to produce new myonuclei, Hikida said.
Myonuclei in muscle cells may be lost during the aging process, and they are not being replaced as readily with new nuclei. This reduction limits how much a muscle can grow.
"Our results suggest that not only are there fewer satellite cells in the elderly, but they have less capacity to be activated and incorporated as myonuclei into the fiber," Hikida said.
The research is part of a three-phase project to study muscle growth. The first phase, which was supported by the NASA Center for Cell Research, involved studies of muscle fibers in rats that had undergone atrophy due to 10 days of spaceflight in the space shuttle Endeavor in 1993. That work suggested that a decrease in muscle mass was associated with a corresponding loss of myonuclei.
The second and third phases of the project involved a study of 10 men age 64 to 70 and 11 men age 22 to 24. During a 16-week period, some of the older men took part in a strength training exercise routine. At the end of the program, researchers examined muscle tissues from all the men in the study. They found that the muscle fibers of older men who exercised during the project only grew to the size as the muscle fibers of the younger men who hadn't started to exercise.
"The muscle fiber size only increased to the size of the sedentary young men," Hikida said. "This suggests that the amount of muscle growth is limited by the number of satellite cells in the muscle fibers, which seems to decrease as people age."
Other study authors included Fredrick Hagerman, professor of physiology, and Robert Staron, associate professor of anatomy, both at Ohio University; Steven Shell, a medical student in the College of Osteopathic Medicine at Ohio University; Sandra Hervey, a former student at Ohio University, now at Wright State Medical School; and Erika Kaiser, a student at Wesleyan University in Connecticut.
Contact: Robert Hikida, 614-593-2323; hikida@ohiou.edu
Written by Kelli Whitlock, 614-593-0383; kwhitlock1@ohiou.edu