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Lifelong exercise protects older adults from losing muscle mass and function with age.

With age, muscles shrink in size and lose strength, a process called sarcopenia that can increase frailty and reduce the quality of life for older adults. In people with sarcopenia, muscle fibers contain fewer satellite cells (i.e., muscle stem cells) and progressively lose their connections to nerves, a process called denervation. Findings of a new report show that lifelong exercisers have more youthful muscles that resist denervation.

Satellite cells are stem cells that proliferate, fuse together, and form the long tubular structures than comprise muscle fibers. Satellite cells are necessary for muscle repair and growth after exercise, a process called hypertrophy, due to their connection with cells that produce growth factors and deliver nutrients. Previous research demonstrates that exercise interventions that last several weeks can reverse muscle denervation in older adults with frailty; however, the preventive effects of lifelong exercise have yet to be investigated.

The authors recruited 15 moderately active young men (average age, 26 years), 16 older men who were lifelong exercisers (average age, 73 years), and 15 older men who lived a sedentary lifestyle (average age, 73 years). On their first visit to the lab, participants completed a bout of heavy resistance training on only one side of their body so that the researchers could compare the effects of exercise and sedentary behavior in each person. The researchers also measured maximum muscle strength and body composition and collected a blood sample. Participants provided another blood sample two days and six days after the exercise challenge and provided a muscle biopsy sample six days after.

Lifelong exercisers had muscles that were more resistant to fatigue during exercise compared to sedentary young and older adults. Compared with sedentary older adults, lifelong exercisers had more satellite cells in their muscles connected to type 2 myofibrils, which are important for fast-twitch muscle movement, but no difference in connection to type 1 slow-twitch myofibrils. Muscles from lifelong exercisers also expressed high levels of mRNA for acetylcholine receptors, which are necessary for preventing denervation.

These results show that lifelong exercisers maintained a more youthful muscle profile due to increased connections with muscle- and nerve-supporting satellite cells. People who started life with a sedentary lifestyle can still reap the longevity-promoting benefits of exercise. Starting a new aerobic exercise habit, even at age 70, cuts heart disease death in half.

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