Mechanical loading from muscle contraction stimulates osteoblast activity to increase bone mineral density.

Study: Effect of Aerobic or Resistance Exercise, or Both, on Bone Mineral Density and Bone Metabolism in Obese Older Adults While Dieting: A Randomized Controlled Trial

When older adults lifted weights while losing weight, they lost much less bone density than those who only walked. This suggests that the force from muscle contractions during weightlifting helps protect bones by keeping bone-forming cells active.

Study: Effects of a 12‐Month Supervised, Community‐Based, Multimodal Exercise Program Followed by a 6‐Month Research‐to‐Practice Transition on Bone Mineral Density, Trabecular Microarchitecture, and Physical Function in Older Adults: A Randomized Controlled Trial

When people do exercises like lifting weights or standing on one leg, their muscles push on their bones, and this makes their bones stronger over time. This study showed that older adults who did these exercises had 1% stronger bones in their spine and hip.

Study: Bone Mass, Density, Geometry, and Stress–Strain Index in Adults With Osteogenesis Imperfecta Type I and Their Associations With Physical Activity and Muscle Function Parameters

When muscles pull on bones during movement, it helps bones get stronger—and this study found that people with stronger muscles tend to have stronger bones, but only if their bones are healthy. In people with a bone disorder, this connection breaks down.

Study: High‐Intensity Resistance and Impact Training Improves Bone Mineral Density and Physical Function in Postmenopausal Women With Osteopenia and Osteoporosis: The LIFTMOR Randomized Controlled Trial

When older women did intense weightlifting and jumping exercises, their bones got stronger and denser — while those who did light exercise lost bone. This shows that strong muscle forces from exercise help build bone.