Muscle memory can refer to motor skills, or it can refer to how muscles recover from atrophy:
Muscle cells are huge, [Kristian Gundersen, a physiologist at the University of Oslo in Norway] says. And because the cells are so big, more than one nucleus is needed to supply the DNA templates for making large amounts of the proteins that give muscle its strength. Previous research has demonstrated that with exercise, muscle cells get even bigger by merging with stem cells called satellite cells, which are nestled between muscle fiber cells. Researchers had previously thought that when muscles atrophy, the extra nuclei are killed by a cell death program called apoptosis.
In the new study, Gundersen’s team simulated the effect of working out by making a muscle that helps lift the toes work harder in mice. As the muscle worked, the number of nuclei increased, starting on day six. Over the course of 21 days, the hard-working muscle increased the number of nuclei in each fiber cell by about 54 percent. Starting on day nine, the muscle cells also started to plump up, adding an extra 35 percent to their volume. Those results indicate that the nuclei come first and muscle mass is added later.
In another set of experiments, the researchers worked the mice’s muscles for two weeks and then severed nerves leading to the muscle so the tissue would atrophy. As the muscle atrophied, the cells deflated to about 40 percent of their bulked-up volume, but the number of nuclei in the cells did not change.
These results contradict previous studies that show lots of cell death in muscles during atrophy. Gunderson’s team examined individual cells in the wasting muscles and found that there is apoptosis going on, but that other cells are dying, not the muscle fibers or their extra nuclei. The extra nuclei stick around for at least three months — a long time for a mouse, which lives a couple of years on average, Gundersen says.
“I don’t know if it lasts forever,” he says, “but it seems to be a very long-lasting effect.” Since the extra nuclei don’t die, they could be poised to make muscle proteins again, providing a type of muscle memory, he says.
(Hat tip to Buckethead, who’s getting back into shape and considering starting his son on lifting.)