Bone gains and losses follow seasonal training and detraining in gymnasts

The response of the human skeleton to high magnitude loading and unloading is poorly understood. Our aim was to evaluate chan-es in bone mineral densi ty (BMD) in a group of intercollegiate gymnasts (n = 8, age = 18.6 0.8 year s) over 24 months that included two 8-month competive seasons and two 4-mon th offseasons. BMD of the hip, spine, and whole body was evaluated by DXA ( Hologic QDR-1000/W) at baseline, 8, 12, 20, and 24 months. Results indicate d significant seasonal trends in BMD of the femoral neck, trochanter, total hip, lumbar spine, and whole body. Specifically, there was a strikingly co nsistent pattern of bone density increases over the training seasons follow ed by clear declines in the offseasons. Increases at the spine were 3.5% an d 3.7% followed by declines of 1.5% and 1.3% in the offseasons. Total hip B MD increased 2.3% and 1.9% during the competitive seasons followed by decre ases of 1.5% and 1.2% in the offseasons. We observed a significant 24-month increase of 4.3% in spine BMD but no significant overall change at the hip . In conclusion, the human skeleton demonstrated a measurable response to h igh magnitude loading and unloading that was consistent across bone sites o ver 24 months of observation.