Growing bones: how important is exercise?

Mouse shoulder morphology responds to locomotor activity and the kinematic differences of climbing and running

Mechanical loads play a significant role in determining long bone shape and strength, but less work has explored how these loads influence flat bones like the scapula, which has been shown to vary with locomotor preference among primate taxa. Here, we tested the effects of voluntary running and climbing exercise in mice to examine how the mechanical loads borne from different locomotor patterns influence shoulder morphological development. Ninety-nine female wild-type mice were distributed equally among sedentary control, activity-wheel running, and vertical climbing experimental conditions. Running mice had the lowest body masses, larger intrinsic shoulder muscles, and the most pronounced differences in scapular size and shape relative to the other groups. Climbing mouse scapular morphology also differed significantly from the control individuals, but these differences were not as marked as those between the running and control mice. This might be attributable in part to greater levels of activity in the wheel-runners relative to the climbers. Additionally, climbing mice held their bodies closer to the substrate and maintained more flexed limbs and posterior hand positions compared with the kinematics of running. As a result, climbers differed significantly from both the running and control mice in developing a relatively broader infraspinous region, which is likely related to preferential recruitment of the infraspinatus and teres minor muscles to maintain flexed shoulder postures. The results of this study demonstrate that variation in activity level and type of locomotor regime over a significant portion of the life history influences muscle and bone development in the shoulder.

State of the Art Reviews: Development of Fitness in Children: The Influence of Gender and Physical Activity

The influences of gender and physical activity on the development of fitness are reviewed from early childhood to late adolescence. Changes in parameters of fitness prior to puberty are driven predominantly by neuroendocrine-mediated factors, although physical activity level may be influenced largely by sociocultural factors prior to and following puberty. Thus, it is still unclear to what extent environment versus genetics accounts for gender differences in fitness. Future studies need to account for all factors known to explain gender differences in fitness to better differentiate intrinsic versus environmental causes. Consequently, one must consider if and to what extent a gender comparison study actually reveals true, inherent gender differences compared with sociocultural and/or cultural influences. Nevertheless, differences in fitness between girls and boys that are influenced by sociocultural factors should be considered when devising programs to promote physical activity and enhance fitness in youth. Fundamentally, the role of parents and primary caregivers in modeling physical activity and influencing the fitness level of their child cannot be overestimated.