Bones are not static. Certain cells called osteoblasts constantly bring calcium into bones to make them stronger and osteoclasts take calcium from bones. Exercise increases the rate that osteoblasts strengthen bones. Inactivity slow osteoblastic activity to weaken bones. So any exercise that places force on a bone will strengthen that bone.
If they live long enough, every woman and most men will suffer from osteoporosis. Women who break their hips from osteoporosis must have a hip replacement immediately. Otherwise, they have a 20 percent chance of dying from complications within a year. A study from Australia shows that running strengthens the leg bones of both older and younger women ( Medicine & Science in Sports & Exercise, October 2005.) However, the research shows that bones used in an exercise are the only bones that are strengthened by that activity. So running strengthens leg bones, rowing strengthens arms and back, and lifting weights strengthen bones that are used for each lift.