Doing intense interval workouts for 8 weeks can change how your genes are switched on or off in your muscles — and this study says it affects over 14,000 spots in your DNA.

When people do long-term workouts like running or lifting weights, their muscle cells show tiny changes in a biological tagging system called DNA methylation—mostly fewer tags in areas that control metabolism and muscle function.

When you do short bursts of intense exercise like sprinting or HIIT, it changes how your muscle genes behave in a way that sticks around—even after you stop exercising for three months—and comes back when you start again.

After young adults stop working out intensely for 12 weeks, their muscles still keep certain chemical 'tags' that changed during training—even though their muscle energy function goes back to normal.

Even if your muscles don't get stronger or fitter after working out again, your body might still remember the old workout at a molecular level—like a biological bookmark keeping track of past exercise.

After just one workout like running or cycling, your muscles quickly change how their genes are turned on—specifically, a gene called PGC-1α gets more active because a chemical tag on it gets removed, helping your body respond to the stress of exercise.