Lust is an energy that needs to be controlled by your inner self. Lust is not a sin. For it to be a sin, it will depend on where you have directed it. If lust makes you think about sex, you have committed the sin of adultery. Likewise, if lust is directed toward physical exercises and just keeping yourself busy, you won't be counted as a sinner. Remember, according to the 2nd Principle of Thermodynamics, energy cannot be created or destroyed, but it can be transformed from one form to another. Think about lust (energy), which cannot be created (something you already have) or destroyed (no way to get rid of lust), but can be transformed from one form to another (depends on where you want to deposit it)."