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While exercise can be prescribed for improving cardiovascular and muscle health, no prescription exists for increasing bone mass. Because bone deformation rate has been identified as an important variable related to osteogenesis, estimates of skeletal loading during human activities likely characterize the associated osteogenic stimulus. However, estimates of body segment parameters (BSPs) are needed to calculate skeletal loading. The preferred equations for calculating pediatric BSPs are based on 12 boys and have not been validated. To validate these equations for girls, we investigated whether equation-estimated BSPs differ from those derived using magnetic resonance imaging (MRI) and whether such differences cause differences in calculated joint kinetics during walking, running, and drop landings from three heights. We further compared hip joint kinetics among activities and to those at the ground. Left leg BSPs were estimated from MRI and using the equations in 10 girls. Joint kinetics were also calculated for each activity from recorded kinematics and ground reaction forces. With the exception of two shank variables, BSPs differed between methods. However, while these differences resulted in statistically significant differences in joint kinetics for all activities, the differences were not sufficiently large to be of practical significance. Thus, equation-estimated BSPs appear suitable for use with girls. Significant relationships were found between peak forces and loading rates at the ground and hip, indicating that resultant hip loads can be predicted using forces at the ground. Walking and landings from 61cm had the lowest and highest forces, respectively. Forces during drop landings increased as height increased. Peak forces during running were not different than those for landings from 30 and 46cm. Loading rates at the ground during walking were less than for other activities, while those during running were less than for drop landings. There were no differences in loading rates among drop landings. Drop landings appear to have the characteristics most likely to cause osteogenesis. By quantifying ground forces and loading rates, we have provided a simple method for quantifying forces at the hip, a necessary step toward a better understanding of the relationship between loading and changes in bone mass at this site. |
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