Image courtesy Hotel de la Paix Genève and Flickr Creative Commons

It has long been known that exercise reaches aspects of health from cardiovascular fitness to  sex drive, and new research reveals that physical activity has the ability to change the very building blocks of human DNA.

Scientists from Stockholm's Karolinska Institute determined through biopsies of muscle tissue that exercise modifies the chemical and structural properties of DNA, engaging genes that help muscles become accustomed to strenuous movement. According to the study, the biochemical process of methylation produces a tag that flips the genetic switch.

Sciencenews.org reports:

Scientists analyzed biopsied cells from thigh muscles of adults who had completed low- and high-impact cycling workouts. After the more strenuous workout, muscle cells had fewer methyl groups attached to DNA and higher levels of blueprints for energy-regulating proteins compared with cells that had undergone a low-impact workout.

Changes were seen almost immediately after the generally inactive subjects completed exercise.  

Physical activity is believed to enhance the body's production of endorphins and norepinephrine, relieving symptoms of depression, lowering blood pressure, and improving the immune system; the study suggests that the relationship between health and the body's chemical operations reaches to the genetic code.

In a Foxnew.com article, study leader Juleen Zierath said:

Our muscles are really plastic. We often say 'You are what you eat,' well, muscle adapts to what you do.  If you don't use it, you lose it, and this is one of the mechanisms that allows that to happen.

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