Weight-bearing physical activity plays an important role in bone health across the lifespan. During childhood, short bouts of high-impact activity augment bone-mass accrual and enhance bone's structural characteristics that contribute to overall bone strength. Along the age continuum, physical activity in adulthood serves to maintain bone mass and strength and in later life, to diminish bone loss. While the specific exercise prescription for bone strength in women and men is not known, a combination of resistance training and impact exercise may offer the best strategy to promote bone health in older adults and ultimately, reduce fracture risk. In this review we discuss the central role that physical activity plays in promoting bone health across the lifespan. Specifically, we focus on the adaptations in bone structure and strength to weight-bearing physical activity.