Physical activity and regional bone mass

Abstract: This thesis considers the effect of physical activity on bone mass in weight-loaded and unloaded regions of the skeleton. Bone mass was measured by Dual X-ray Absorptiometry (DXA) and by Quantitative Ultrasound (QUS). In a cross-sectional study 67 male soccer-players, on different levels of the Swedish national league, were compared with 24 male controls. No differences were demonstrated between soccer-players on different exercise levels, but the soccer-players had 13% higher bone mass in the hip and 24% higher value in the calcaneus compared with the controls. Bone mass was correlated with duration of exercise up to 6 hours per week, but further increase in exercise did not confer additional bone mass. It seems as bone mass increases to a level sufficient to maintain the bone strength that is required. The bone mass was 10% lower in the upper part of the skull, an unloaded skeletal region, in the soccer-players compared with the controls. Furthermore, 128 male former soccer-players (20?85 years) were compared with 138 matched controls. No differences were demonstrated in bone mass after the age of 70 years either in the skull or the hip when comparing former soccer-players and controls. In a longitudinal study 32 women and 12 men who had sustained a hip fracture were followed 1 year after the injury. The bone mass decreased in the fractured femur by 14% and in the non fractured hip by 4% while the bone mass increased in the upper part of the skull by 4% during the 13 months follow-up. It seems as bone mass in the upper part of the skull, an unloaded region, is affected in an opposite direction compared with bone mass in weight-loaded regions of the skeleton, in periods of increased as well as decreased activity. Athletes with medial tibial stress syndrome had 15% lower bone mass compared with controls in the tibial region corresponding to the pain, but higher bone mass in virtually all other weight-loaded regions. Fourteen of the athletes with medial tibial stress syndrome were re-measured after 6 years when all had improved. The bone mass in the tibial region corresponding to the pain had then increased by 19% so that no difference could be detected compared with controls. In the other weight-loaded regions bone mass was unchanged. It seems as protracted medial tibial stress syndrome affects the skeleton but the bone mass normalises with recovery from symptoms.