"Be transformed by renewing your mind"
Exercise is definitely for the body: however, it is a Pillar of the Mind for many reasons. It aids in blood flow to the brain: it release endorphins which aid in relieving the brain of stress, and it can be used to build those aspects of the mind such as determination, discipline, courage, and confidence.
Exercise can be any activity that moves the body, but exercise discipline affects the mind differently. For example, if one is training to enter the military, their mind will develop different attitudes compared to one who chooses to walk a mile a day. It is important to know your goals before choosing any certain Exercise Pillar option. Knowing your goals will help you determine what to pick. Whatever it is, make the decision and stick with it for it will build those aspects of the mind that will affect your whole life.