Lets talk about the mental impact and exhilaration of competition and what that does to the male libido. The psychic and emotional energy associated with physical activities makes for a well rounded person.
Fitness contributes to a happy marriage, more so than counting pennies and obsessing over .50 gains and losses.
Out to train for the next race!
Oh, and mountain biking is very low impact to nature, certainly less than cattle grazing.