GROUND REACTION FORCES PRODUCED BY JUMPING ACTIVITIES FOR BONE ACCRETION IN SCHOOL-AGE CHILDREN

Establishing an optimum level of bone during the growing years is a critical step in the prevention of osteoporosis and subsequent fractures later in life. Performing activity that is weight-bearing or impact-loading (ground reaction forces 4–12 times body weight) is one of the most effective ways to promote bone accretion. However, excessive impact loading forces (> 10 times body weight) have been implicated in the etiology of lower extremity repetitive injuries and osteoarthritis. Most studies in this area have focused on the effect of specific sports training on bone, but there is clearly a need to develop and evaluate activities that can be performed as part of a wide-reaching, community-based physical activity program with optimal levels of impact forces. The aim of this study was to test the force generated by specific jumping and hopping activities performed by 5–9 year olds (N = 12). Ground reaction forces were measured using a tri-axial, piezoelectric force plate at 200 Hz during 12 jumping and hopping activities. The activities included common childhood activities such as jumping off steps of varied heights, vertical and broad jumping, hopping, jumping jacks and jumping rope. Descriptive statistics were completed on the magnitudes of impact forces from 10 jumps/hops, normalized to body weight. All activities generated impact forces over 4 times body weight, jumping from taller vertical heights (≥ 60 cm) or with instruction to more actively jump resulted in impact forces > 10 times body weight. Our work suggests that common childhood jumping and hopping activities can generate sufficient impact force for bone accretion, however excessive impact forces are produced at higher vertical heights, and an instruction dependence exists. Supported by NIH (NICHD) RO1 HD37752-01