Most athletes are familiar with the phenomenon known as “muscle memory,” which is the ability of an inactive previously trained individual to quickly return to an elevated level of muscular function and size once regular exercise is resumed. The mechanisms responsible for muscle memory have never been clear, but were often assumed to be related primarily to the influence of exercise on muscle neural pathway development.
A recent study* however has revealed evidence of changes in the muscle cells themselves that might be a key to the muscle memory phenomenon. In the study the authors show that the extra myonuclei generated in response to overload exercise are in large part retained even in periods of disuse atrophy.
Myonuclei serve as the “command control centers” so to speak that govern the synthesis of proteins that are used to make your muscles bigger and stronger in response to exercise. When you work out, your body responds by first increasing the amount of myonuclei (obtained through the recruitment of satellite cells) in the muscle cells, and then these new myonuclei ramp up the production of muscle proteins. When you stop training though you lose muscle protein (muscle size), however the increased number of myonuclei (according to this study) seem to stay put. As a consequence, your body is already equipped to respond quickly to renewed exercise stress with fast hypertrophy and functional improvement (i.e. muscle memory).
The consequences of this phenonemon in the prevention of age related muscle loss is noted by the authors, who mention the fact that incorporation of new myonuclei in aged humans is greatly compromised. The authors also make note of the significance of this mechanism for anabolic steroid users. Since incorporation of extra myonuclei is a major mechanism through which anabolic steroids increase muscle size, it seems plausible that this has a lot to do with the observation that former steroid users seem to maintain some level of permanent performance advantage over steroid novices.
Proc Natl Acad Sci U S A. 2010 Aug 24;107(34):15111-6. Epub 2010 Aug 16., Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining, Bruusgaard JC, Johansen IB, Egner IM, Rana ZA, Gundersen K.