You are either freed or confined by your thoughts...do you believe that? The beliefs that you have about what you are capable of IS your reality. Do you believe that you are, or can be, strong? Healthy? Confident? Happy? These beliefs don't just happen, just like health doesn't just happen. They both are the outcome of repetition; thinking thoughts which propel you to success (or re-directing your negativity) and repeatedly moving your body through exercise.
Trust that you are capable of both physical and mental well-being. It simply takes practice.