The healthy body creates free radicals as a result of normal activity & metabolism. These free radicals, known as ROS (reactive oxygen species) or RNS (reactive nitrogen species) are kept in check by the healthy body, maintaining normal mitochondrial function and minimizing oxidative stress.
Healthy and unhealthy individuals create oxidative stress. Exercise increases a person’s use of oxygen, and increases the work load on the mitochondria. As a result, professional athletes create higher oxidative stress (free radical activity) levels than those who do not exercise to the same extreme. Those facing health challenges may promote a less than optimal level of oxidative stress. The point is that oxidative stress occurs on an ongoing basis and for a variety of reasons.