Influence of isotonic, isometric and isokinetic muscle strength on bone mineral density of the spine and femur in young women

Bone mineral density (BMD) is dependent on multiple influences including genetics, mechanical forces, hormonal changes and nutritional mechanisms. The mechanical forces are, in part, influenced hy muscle strength. This study examined the relationships between BMD of the spine and femur with muscle strength. Eighty-one healthy, non-athletic women aged 20-30 years were the subjects in the study. BMD was measured by dual energy x-ray absorptiometry. Trunk strength was measured by a Wagner Dynamometer or a Cable Tensiometer and leg strength was measured with a Cybex II isokinetic dynamometer. Trunk, leg and hip strength was also measured using IRM (one repetition maximum). There were significant correlations between spine density and trunk extension (r = 0.40, P = 0.0001) and spine density and trunk flexion (r = 0.30, P = 0.0037). There were significant correlations between femoral neck density and knee extension (r = 0.40, P = 0.003) and femoral neck density and knee flexion (r = 0.24, P = 0.0240). Multiple regression analysis showed that amongst young adult females weight and trunk extensor muscle strength contributed about equally to spine density. Flexor muscle strength did not influence bone density.