You don't exercise in your free time, just like you don't work in your free time.

edit: No, I do it in the time I set aside to exercise.

This might seem foreign to you but to me it's no different from someone saying "I need £100 to pay the rent" and so they make time and find a way to pay the bills (usually a job). They don't "work in their free time", they structure their life around it because income is important to them.