Lapsed lifters and former triathletes love to crow about how—right now!—they could hit the gym and toss up massive weight or easily get back in shape because they have superior "muscle memory." For endurance athletes specifically, muscle memory translates to muscle that is more energy-efficient. According to an old myth, if an endurance athlete has been in shape in the past, it's easier for them to get fit again after an extended period of no training thanks to this "muscle memory."

Not so, says a recent study published in PLOS Genetics: it found that the muscles of sedentary people who trained for three months showed positive genetic changes, and then after taking nine months off those changes were gone, suggesting effects of exercise don't stick with muscles for long. 

To conduct the research, study author Maléne Lindholm of the Karolinska Institute in Stockholm and his team analyzed the results of a 15-month endurance training experiment, in which 23 volunteer subjects spent the first three months training four times a week—kicking one leg 60 times per minute for 45 minutes—and resting the other leg. (We wonder if they at least got to watch TV while they performed this mundane task...)

To establish a baseline, Lindholm and his team sampled muscle biopsies before and after the three-month training period and found that genes associated with energy activity had positively changed in the leg that had performed the endurance training.  Then, after nine months of no endurance training, researchers took biopsies from the thighs of 12 of the original subjects and found that "the training effects were presumed to have been lost," according to Lindholm. This means that there were no significant differences in gene activity between the previously trained legs and the sendentary legs. Finally, the same 12 original subjects completed a three-month training period in which they exercised both legs and researchers saw no difference in gene activity between the previously trained leg and untrained leg.

It's important to note, however, that although this study found that muscle memory may be a myth for endurance athletes in particular, this research has “no bearing on the possible memory in other organ systems,” according to physiologist Kristian Gundersen. That means it's very possible that organ systems such as the heart and cardiovascular systems could remember and allow athletes to regain previous fitness levels more easily. It's also possible that cells within the muscle tissue, such as stem cells or immune cells not studied in this experiment could also perform some memory function. 

So instead of getting lazy during the winter and relying on your muscle memory to bounce back in the spring, check out 5 ways to not slack off on running when it's cold outside. But don't stress too much if you take off a week or two from exercise every once in a while, experts say that infrequent breaks from training won't cause you to lose muscle or fitness—so long as they don't go on too long!