Yes, I believe it would be a sin.
Didn't Paul teach about us all running in a race?
That all Christians and churches should be involved in having foot races from time to time?
Each denomination should have it's own running program. Just kidding.
For bodily exercise profiteth little: but godliness is profitable unto all things, having promise of the life that now is, and of that which is to come.
For bodily exercise profiteth little: but godliness is profitable unto all things, having promise of the life that now is, and of that which is to come.
First Timothy 4:8 informs us, “For physical training is of some value, but godliness has value for all things, holding promise for both the present life and the life to come.” Notice that the verse does not negate the need for exercise. Rather, it says that exercise is valuable, but it prioritizes exercise correctly by saying that godliness is of greater value.
The apostle Paul also mentions physical training in illustrating spiritual truth in 1 Corinthians 9:24-27. He equates the Christian life to a race we run to “get the prize.” But the prize we seek is an eternal crown that will not tarnish or fade. In 2 Timothy 2:5, Paul says, “Similarly, if anyone competes as an athlete, he does not receive the victor's crown unless he competes according to the rules.” Paul uses an athletic analogy again in 2 Timothy 4:7: “I have fought the good fight, I have finished the race, I have kept the faith.” While the focus of these Scriptures is not physical exercise, the fact that Paul uses athletic terminology to teach us spiritual truths indicates that Paul viewed physical exercise, and even competition, in a positive light. We are both physical and spiritual beings. While the spiritual aspect of our being is, biblically speaking, more important, we are to neglect neither the spiritual or physical aspects of our health.