Site-specific bone mass differences of the lower extremities in 17-year-Old ice hockey players

The purpose of the present study was to evaluate bone mass in the pelvis and lower extremities in young ice hockey players, and especially to investigate whether any differences are related to the type and magnitude of weight-bearing loading and muscle stress. The ice hockey group consisted of 22 boys (mean age 16.9 +/- 0.3) from three different ice hockey teams training for about 9 hours/week (mean 9.3 +/- 2.0, range 6-15). The reference group consisted of 22 boys (age 16.8 +/- 0.3) not training for more than 4 hours per week (mean 1.5 +/- 1.5, range 0-4). The groups were matched according to age, pubertal stage, weight, and height. Areal bone mineral density (BMD) was measured in total body, head, pelvis, ala ossis ilii, femoral neck, trochanter, femur diaphysis, and tibia diaphysis using dual energy X-ray absorptiometry. Isokinetic muscle strength of the quadriceps and hamstrings muscles was measured using an isokinetic dynamometer. BMDs of the total body, femoral neck, trochanter, and pelvis, but not of the head, ala ossis ilii, femur diaphysis, and tibia diaphysis, were found to be significantly higher (P < 0.05) in the ice hockey group. Muscle strength of the quadriceps muscles was also found to be significantly higher among the ice hockey players, but this greater muscle strength did not predict any BMD site significantly. However, in the reference group, there was a general strong relationship between muscle strength and BMD. This study has demonstrated significantly higher BMD in adolescent ice hockey players than in referents on a low or moderate level of physical activity. The differences seem to be site-specific and may be related to the type and magnitude of loading acting on each site, during off-season training and preferentially during ice hockey. The nonsignificant differences in BMD of the tibia and femur diaphyses may reflect that the compressive forces acting on these sites during ice hockey are not of sufficient magnitude to influence BMD. High muscle stress in itself, without weight-bearing loading, acting on the ala ossis ilii in adolescent boys does not seem to increase BMD, and an increased muscle strength does not predict BMD in highly trained adolescent boys.