Impact Exercise for Optimal Bone Health in Growing Children: An Evidence-Based Approach to Exercise Prescription

Abstract

The nature of bone to adapt to mechanical loading is well accepted. Bone responds to increased mechanical strain by growing in size, gaining strength, increasing mineral content, and favorably altering bone structure. Physical activity imposes substantial mechanical strain through muscle and gravitational forces. Thus it follows that bone should grow favorably in its mass and structure to accommodate increased loads from physical activity. Data support that children who are physically active have enhanced bone mass and bone structure compared to less active peers. Physical activities shown to have the greatest osteogenic effects in the growing skeleton are those that have a significant “impact factor.” Impact activities are characterized by both the speed of loading and the magnitude of the load applied to bone. Greater forces, delivered quickly, through activities such as jumping appear to convey the greatest benefits to bone mass and size during growth, although resistance training may also elicit favorable development. Exercise interventions utilizing impact exercises report skeletal benefits when children achieve ground reaction forces three to eight times their body weight. Research thus far indicates that at least 7 months of impact exercise is essential to induce a measurable change in bone mass in children. For optimal bone growth, children should perform impact activities 3 days per week for 10–20 min; however, if they are to rely on typical playground activity it seems that 30–40 min of vigorous activities are necessary. Exercise performed during time of growth induces lifelong benefits suggesting there is a “window of opportunity” during pre- or early pubertal years to maximize skeletal growth and reap enduring benefits that will lower risk of fracture and osteoporosis during life as an adult. This chapter will explore the influence of impact exercise during growth on bone mass accrual and structure; present the available data regarding optimal exercise prescription, including timing and dose; and explore the potential for physical activity undertaken during childhood to mediate osteoporosis later in life.