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Disseration, 2002;

Effect of Exercise on Bone Mass and Structure with Special Reference to Maintenance of the Exerciseinduced Bone Gain

Jahr: 2002

Kontulainen S
Faculty of Sport and Health Sciences of the University of Jyväskylä


The primary findings and conclusions of the present series of studies can be summarised as follows:
Studies I and II demonstrated that long-term racquet sports training had increased bone mineral mass and built a stronger bone structure at the loaded arm’s proximal humerus, humeral shaft, distal humerus, and radial shaft mainly by increasing the bone size, not the volumetric density of the cortical bone. In fact, the density of the cortical bone in these bone regions was slightly but systematically greater in the lessloaded bone site in players, as well as in the nondominant arm of the controls. The greater bone size at these loaded bone sites was due to enlargement of the periosteal surface of the cortex. At the male players’ proximal humerus and radial shaft, the area of marrow cavity was also greater at the loaded bone site. At the distal radius, besides the somewhat enlarged bone size, the trabecular density at the loaded bone site was increased in the female players. To conclude, playing long-term racquet sports had increased bone mass in the loaded upper arm mainly via periosteal enlargement of the cortex, and thereby built a stronger structure of bone at the loaded site.
In both of the female player groups the structural adaptation to the longterm loading was achieved through the above noted periosteal enlargement of the bone cortex at the humeral shaft. However, this adaptation was two times better in those players who have started playing before or at puberty rather than after it. Comparison of this exercise-induced benefit in terms of bone strength between the young and old starters was even greater than the gain in bone size. Exerciseinduced enlargement in bone size was not so clear at the distal radius. Indeed study II suggested that at the ends of long bone the apparent trabecular density might increase in response to long-term loading. These results emphasize the importance of exercise during the growing years - not only to enhance the accrual of the peak bone mass but especially to increase bone size and thus, improve bone strength, a key component of fracture prevention.
Studies III and IV examined whether or not the bone benefit achieved by playing racquet sports is maintained despite 4 and 5 years of reduced training. These studies indicated that the exercise-induced bone gain was well maintained in male players and in both groups of female players regardless of their clearly different starting age of activity and the magnitude of the exercise-induced bone gain. Thus, the results did not support the notion that the exercise-induced bone gain that is obtained during the growth may better withstand the effects of decreased training than the bone gain obtained later in adulthood.
Consistent with the above noted maintenance of the exercise-induced benefit after reduced racquet-sports training, study V showed that the positive effect of 9-month jumping intervention on bone accrual in growing girls was maintained at the lumbar spine a year after the end of the intervention. At the hip, bone mineral accrual was also in favor of the former trainees but these differences were statistically insignificant. The difference between the former trainees and their controls in the improvement of the explosive type of muscle strength was noted, in favor of the trainees, during the follow-up. Finally, the 5-year follow-up
study (VI) of the premenopausal women showed good maintenance of the training-induced bone benefit in the former trainees compared to their controls during a detraining period of three and half years. In contrast, the post-intervention differences in physical performance tests between the groups, in favor of the trainees, were lost during the same period of detraining. Thus, study VI suggested that the high-impact activity-induced bone benefit in premenopausal women could be maintained with ordinary, low-impact type of activities only. This is an important consideration when evaluating the feasibility and long-term
utility of training interventions among adult women.

Schlagworte: Bone Training
GID: 671; Letzte Änderung: 07.01.2008
Weitere Informationen: Original Article