He's now having trouble with his feet, of all things. The pleasant young podiatrist showed him the x-rays of his feet, and pointed out a certain curvature of his metatarsal bones.
"At some point you've had stress fractures here, and here.", while pointing at each foot.
It is similar to people lifting a lot of weight to get fit. BTW, weight training alone is not sufficient IMO. You need to add cardiovascular training as well.
So, the best solution is exercise in moderation and balance (a mix of aerobic and anaerobic exercise with an emphasis on aerobic).