You might think of your bones as not changing once you’re done growing, but they constantly change through a process called bone remodeling. During bone remodeling, bone cells absorb old or damaged bone tissue, then new bone cells deposit new tissue. In the late 19th century, German surgeon Julius Wolff described how bones adapt to stress, known as Wolff’s law. For example, if you frequently lift heavy objects, your bones will strengthen over time. Conversely, if you don’t use a bone, it will weaken. Wolff’s law applies to physical therapy, preventing osteoporosis, and treating fractures. Physical therapy involves exercises, stretching, and massage to restore strength and mobility. Therapists design recovery plans based on Wolff’s law. If you break a leg, your therapist will introduce weight-bearing exercises to help the bone remodel, starting with simple tasks and progressing to more challenging ones. Osteoporosis makes bones porous and fragile, increasing fracture risk. Preventing osteoporosis involves regular weight-bearing and muscle-strengthening exercises to maintain bone mass. If you have osteoporosis, consult your doctor before new exercises. Bone fractures are treated by immobilizing the area with a cast or splint. Although immobilization weakens bone tissue, once the cast is removed, gradual weight-bearing exercises help strengthen the bone through remodeling.