Q: My knees and hips hurt when I do weight-bearing exercise like running or playing basketball. So instead, I punch a speed bag, which works only my arms and shoulders. Will that help improve my bone density overall, including in my legs?
A: No. The benefit is site-specific, so that when you run, the bone growth occurs primarily in your legs and hips; when you hit a speed bag (assuming you aren’t moving around a lot), the effect is in your upper body.
Bone-healthy “weight-bearing” exercise involves anything you do against the force of gravity—usually exercise done while on your feet, such as running, basketball, stair climbing, and dancing. Activities involving muscle force also stimulate bone building. That includes strength training and exercise such as hitting a speed bag.
When bones are put under strain, this triggers specialized cells to build bone. The more load on the bone, the greater the benefit. Thus, high-impact or resistance workouts build more bone than low-impact activities.
If you can, do some resistance exercises involving your legs, such as leg presses. Research suggests that short bouts of vigorous weight-bearing exercise can benefit bones. Try to hop or jump even for 5 to 10 minutes; jumping rope is a good option. If that’s too painful, discuss your exercise options with a health care provider or physical therapist.
See also: Tai Chi and Bones.