The old adage, “use it or lose it”, tells us: if you stop using your muscles, they’ll shrink. Until recently, scientists thought this meant that nuclei — the
cell control centres that build and maintain muscle fibres — are also lost to sloth. Modern laboratory techniques now allow us to see that nuclei gained during training persist even when muscle cells shrink due to disuse or start to break down. These residual ‘myonuclei’ allow more and faster growth when muscles are retrained, suggesting that we can “bank” muscle growth potential in our teens to prevent frailty in old age. It also suggests that athletes who cheat and grow their muscles with steroids may go undetected. The findings, by researchers in the U.S., appear in Frontiers in Physiology .