Bill Wilcox:

Not only does exercise add to our free radical load, but normal breathing
adds to our free radical load.  Oxygen fuels our metabolism, but it can also
cause damage through oxidation and free radical formation.  If our world was
less toxic, then the antioxidants found in natural and paleo diets would
probabaly be sufficient to protect us.  I'm not suggesting to anyone to stop
exercising.  The benefits of exercise far outweigh any potential negatives
from increased exposure to oxygen and free radical formations.  However,
since we live in a world different from our paleo ancesters, it's wise, I
believe, to protect ourselves aainst further free radical damage.

Ed Campbell, DC,CSCS