1 Corinthians 9:25-27

Now every athlete who [goes into training and] competes in the games is disciplined and exercises self-control in all things. They do it to win a crown that withers, but we [do it to receive] an imperishable [crown that cannot wither]. Therefore I do not run without a definite goal; I do not flail around like one beating the air [just shadow boxing]. But [like a boxer] I strictly discipline my body and make it my slave, so that, after I have preached [the gospel] to others, I myself will not somehow be disqualified [as unfit for service].