Jogging. I found this answer by process of elimination. Swimming takes a lot of force, like kicking which gives heavy force on bones, jumping rope, (believe it or not) can also affect his bones since he is "pounding" on the ground. Basketball is much like the jumping rope. But jogging is meant to be a light run, and if you jog the right way, (lightly on your feet) you can stay active and avoid heavy force on bones.
A behavior goal you can use is by using motivation and courage to help you out
