When we think of the term “muscle memory”, we likely ponder on the ability to repeat specific motions without really thinking about it; through practice, these movements become faster and more efficient. A brand new study, however, has discovered a very different type of muscle memory – one that exists on a genetic level and one that influences growth.
Writing in Scientific Reports, the team – headed by Keele University – announce that periods of skeletal muscle growth are recorded by the genes within the muscle. These “memories” are encapsulated in chemical tags, which attach themselves to the relevant genes and assist in muscle growth in later life, based on their history.
These tags are referred to as “epigenetic modifications”, and before we go any further, it’s worth remembering what this is referring to.
Epigenetics, a strangely nebulous term, roughly means “outside” or “on top of” genetics. Generally speaking, it describes the effect external or environmental changes have on DNA. In this case, this doesn’t mean the DNA is changing or mutating, though – it merely describes alterations to the way the genes express themselves, or behave, so to speak.
As rather beautifully explained by this piece over on The Conversation, epigenetics is about turning genes on or off. It can explain cellular memory, in that a physical experience a cell has gone through can be “remembered”, chemically speaking, and passed on to its progeny.
That’s what these tags are. They’re additions to the genes, telling them whether to be active or inactive. It wasn’t easy to find them, mind you: over 850,000 sites on various collections of human DNA had to be carefully analyzed to spot them.
For the study, eight healthy males were asked to exercise to increase their skeletal muscle mass for several weeks; they were then given the same period of time to stop exercising, before being asked to engage in another identical time period of exercise. As expected, lean muscle mass increased at first, then returned toward a baseline, then further increased toward the end of the experiment.
Their genomes were picked apart by researchers throughout the experiment, and this is how the epigenetic tags were discovered. The tags seemed to be telling these muscle growth genes to remain inactive, which means that more tags equals less growth.
However, it’s when they appeared and disappeared that really piqued the team’s interest.
“Exercise induced muscle growth actually untagged the DNA more so that more genes could be switched on and help the muscle tissue grow,” senior author Dr Adam Sharples, a senior lecturer in cell and molecular muscle physiology at Keele University, told IFLScience.
“Most staggeringly, the DNA remained untagged on a number of genes even when they stopped exercise and their muscle returned to normal levels.”
Tagging these genes would mean that future exercise would only bring about slow muscle growth, but that’s not what the researchers observed.
“When they exercised and grew their muscle again later, the genes were turned on to an even greater extent, meaning the muscle could grow even more,” Sharples added. This suggested to the team that the genes had “remembered” the previous exercise.
As fascinating as this is in isolation, this could also potentially spell trouble for athletes that engage in doping – taking performance-enhancing drugs. There’s a chance that any drugs that boost muscle growth could also generate specific tags, which could be picked up by later medical checks even if the drugs have left their systems.
Sharples describes this as a “genuine” but “indirect” implication, however, and a “study would need to be done with drugs to confirm this.”