When we exercise bones like part of a mechanical machine is stressed this cause the body to produce and repair any of the bones that are worn off or damaged (machines need human intervention to replace worn parts).
The bone will now be stronger to take more loading and reduce the risk of fracture.
Short intense and frequent exercise is better than prolonged workouts without rest.
Resting is also important between exercise to allow the repair to be made. ( similar to machine scheduled preventive maintenance.
Check your BMI - Body weight(in KG) divide by the square of your Height(in Meters)