...if muscles have been trained in the past, they seem to develop a molecular memory of working out that lingers through a prolonged period of inactivity, and once we start training again, this “muscle memory” can speed the process by which we regain our former muscular strength and size.
Swedish researchers...began by recruiting 19 young men and women who had never played sports or formally exercised at all, so that their muscles were new to formal weight training. They checked these volunteers’ current muscular strength and size, and then had them start training a single leg...one-legged workouts continued for 10 weeks, at which point the researchers re-measured muscles, and then the volunteers stopped their training completely for 20 weeks...After this layoff from working out, they returned to the lab, where the scientists checked the current state of their leg muscles, took muscle biopsies from both legs and had them complete a strenuous leg workout, using both legs this time. Afterward, the researchers biopsied the muscles again. Then they checked the levels of a wide array of gene markers and biochemical signals within the volunteers’ muscle cells that are believed to be related to muscle health and growth.
They found telling differences between the legs that had trained and those that had not, both before and after the lone training session. For one thing, the previously trained leg remained sturdier, having retained about 50 percent of its strength gains during the 20 weeks without exercise.
Taken as a whole..the trained leg’s genetic activity suggests that its muscle cells had become genetically and metabolically more ready to strengthen and grow than the cells in the leg that had not trained before. These findings support the idea that muscle memory can occur at the gene and protein level.