The study suggests even as the ability of muscle tissue to contract reduces with age, exercise prevents its ability to heal after injury from slowing with age.
The study, from McMaster University in Hamilton, Ontario, Canada, was published in The FASEB Journal.
Senior author Gianni Parise, an associate professor in the Department of Kinesiology, says:
"Exercise-conditioning rescues delayed skeletal muscle regeneration observed in advanced age."
In many mammals, including humans and mice, the speed at which muscle repairs itself slows down with age. In fact, at one time, it was thought skeletal muscle was unable to repair completely after a certain age.
Prof. Parise and colleagues found after only 8 weeks of exercise, old mice showed faster muscle repair and regained more muscle mass than same-aged, non-exercised mice.
They suggest the finding is important because it supports the idea that exercise has a therapeutic effect.
For their study, the researchers used three groups of mice. The first was a group of old mice that underwent 8 weeks of progressive exercise.
The second group also consisted of old mice, but they did not undergo any exercise training, and the third group comprised young, non-exercised mice.
Following the exercise period, all the mice were inflicted with muscle injury via injection of a snake venom into their leg muscles (the tibialis anterior).
The team measured the condition of the muscle tissue in the animals before injury, 10 days after injury, and 28 days after injury.
More satellite cells in muscles
Comparison of the results showed the average area of muscle fiber cross-section was reduced in all three groups of mice at day 10; however, by day 28, it was only restored to pre-injury values in the old exercised group and the young, non-exercised group.
The authors conclude that exercise pre-conditioning appears to improve the ability of skeletal muscle to regenerate after injury in aged mice.
Adult muscles contain satellite cells - quiescent stem cells that become active when injury occurs. On activation, they repair damaged muscle and replenish the pool of stem cells.
The researchers found the pre-injury quantities of satellite cells in the animals' muscle fibers was greater in the old exercised mice than in the old non-exercised mice.
Dr. Thoru Pederson, editor-in-chief of The FASEB Journal, says the study is a "clean demonstration" that even in old animals, "the physiological and metabolic benefits of exercise radiate to skeletal muscle satellite cells."
He notes that even as the ability of muscle tissue to contract reduces with age, the capacity of the satellite cells to respond to the effects of exercise appears to be maintained.
"Exercise pre-conditioning may improve the muscle repair response in older adults to stimuli such as acute periods of atrophy/inactivity and/or damage."
Prof. Gianni Parise