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.

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 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.

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.