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Scientists believe that the adage “use it or lose it” could be wrong, with muscle fibre cells gained from past training surviving even during times of disuse.
According to a review published in Frontiers in Physiology, residual muscle cells, known as myonuclei, allow more and faster growth when muscles are retrained. It could have ramifications for health policy, researchers argue.
If muscles are not used they shrink, which led to the belief that nuclei — cell control centres that build and maintain muscle fibres — were lost.
Lawrence Schwartz, a professor of biology at the University of Massachusetts, said muscle growth was accompanied by new nuclei from stem cells to meet the demands of larger muscles. He said it had been assumed that when a muscle atrophied because of disuse or disease the number of myonuclei decreased. But independent studies — one in rodents and one in insects — demonstrated that nuclei remained even after muscle death began. Researchers said this suggested that once a nucleus had been acquired by a muscle fibre it probably belonged for life.
“Muscles get damaged during extreme exercise and often changes in food availability and other environmental factors lead to atrophy,” he said. “They wouldn’t last very long giving up their nuclei in response to every insult.”
Researchers believe that the retention of myonuclei should enable muscle size and strength to be recovered more quickly and help to explain the phenomenon of “muscle memory”.
Professor Schwartz said: “The phrase ‘use it or lose it’. . . might be more accurately articulated as ‘use it or lose it, until you work at it again’.” He said the findings show the value of exercise when young. “During adolescence muscle growth is enhanced by hormones, nutrition and a robust pool of stem cells, making it an ideal period for individuals to ‘bank’ myonuclei that could be drawn upon in old age.”
He argued that the research also supported permanent bans for athletes found to use steroids as they could benefit long after their usage had ended.