Exercise increases free radical production and activates gene programs that enhance antioxidant defenses and improve clearance of damaged proteins and mitochondria.

“During the exercise, it's a major stress on the cells in the muscles. There's a big increase in free radical production. Cells are electrically active, the muscle cells. So, if they contract, so there's ion fluxes that have to be dealt with. However, having been exposed to that stress during the exercise, the cells activate gene programs that help them cope with stress and become stronger and more resilient. So, for example, exercise increases antioxidant defenses in muscle cells. It enhances the ability of the muscle cells to clear out damaged proteins, dysfunctional organelles, such as mitochondria, which are the energy-producing organelle in the cell. And as well, there are proteins that are initially called heat shock proteins, but their function is to protect other proteins from being damaged. So, all of these beneficial mechanisms are stimulated by exercise.”