"We can’t change the genetic code that our parents gave us, but we can change the way we use it. By exercising we can play with the genetic code. And everyone has the potential to switch the desire for exercise on and off." Romain Barres
He found that exercise activates the genes (turned them on) in muscles that prepare them for movement, strength, and energy. When he biopsied muscle tissue before and after exercise, he found chemical changes in genes that code for strength and energy changes. These changes in muscle are needed during movement and exercise. In other words, exercise begets exercise on the genetic level.
This is just another example of how the body is highly adaptable to its environment. However, once the exercise is over, the genes are turned back off again. I think regular exercise probably up regulates the genes more efficiently and trains a better muscle response.
1. Romain Barrès, etal.Acute Exercise Remodels Promoter Methylation in Human Skeletal Muscle. Cell Metabolism, Volume 15, Issue 3, 405-411, 7 March 2012