BONE MASS AND BONE TURNOVER IN POWER ATHLETES, ENDURANCE ATHLETES, AND CONTROLS - A 12-MONTH LONGITUDINAL-STUDY

Strain magnitude may be more important than the number of loading cycl es in controlling bone adaptation to loading, To test this hypothesis, we performed a 12 month longitudinal cohort study comparing bone mass and bone turnover in elite and subelite track and field athletes and less active controls, The cohort comprised 50 power athletes (sprinter s, jumpers, hurdlers, multievent athletes; 23 women, 27 men), 61 endur ance athletes (middle-distance runners, distance runners; 30 women, 31 men), and 55 nonathlete controls (28 women, 27 men) aged 17-26 years, Total bone mineral content (BMC), regional bone mineral density (BMD) , and soft tissue composition were measured by dual-energy X-ray absor ptiometry, Bone turnover was assessed by serum osteocalcin (human immu noradiometric assay) indicative of bone formation, and urinary pyridin ium crosslinks (high-performance liquid chromatography) indicative of bone resorption. Questionnaires quantified menstrual, dietary and phys ical activity characteristics. Baseline results showed that power athl etes had higher regional BMD at lower limb, lumbar spine, and upper li mb sites compared with controls (p < 0.05), Endurance athletes had hig her BMD than controls in lower limb sites only (p < 0.05), Maximal dif ferences in BMD between athletes and controls were noted at sites load ed by exercise, Male and female pou er athletes had greater bone densi ty at the lumbar spine than endurance athletes, Over the 12 months, bo th athletes and controls showed modest but significant increases in to tal body BMC and femur BMD (p < 0.001), Changes in hone density were i ndependent of exercise status except at the lumbar spine, At this site , power athletes gained significantly more hone density than the other groups, Levels of bone formation were not elevated in athletes and le vels of bone turnover were not predictive of subsequent changes in bon e mass, Our results provide further support for the concept that bone response to mechanical loading depends upon the bone site and the mode of exercise. (C) 1997 by Elsevier Science Inc.