1 Corinthians 9:25-29

Everyone who competes in the games exercises self-control in all things. So they do it to obtain a perishable wreath, but we an imperishable.

Therefore I run in such a way as not to run aimlessly; I box in such a way, as to avoid hitting air;

but I strictly discipline my body and make it my slave, so that, after I have preached to others, I myself will not be disqualified.