Lower extremity muscle strength does not independently predict proximal femur bone mineral density in healthy older adults

The relationship described in the published literature between muscle strength and bone mineral density of older adults is not entirely certain. It is possible that the direct relationship reported in some studies is biased by failing to mathematically account for the biological influence of body weight and body height on both bone mineral density and muscle strength. This study sought to determine if the relationships between measures of lower extremity muscle strength and bone mineral density of the proximal femur are independent of body size (i.e., body height and body weight) in healthy older adults. We recruited 50 older women and 29 older men, all of whom were healthy community dwellers and not involved in resistance training. Quantitative analysis of the isometric strength of the bilateral ankle, knee, and hip joints and assessment of bone mineral density of the proximal femur were conducted. Muscle strength values were adjusted for the influence of body height and body weight using an allometric scaling procedure. The correlations between proximal femur bone mineral density and the unadjusted strength values were weak but statistically significant. After adjusting muscle strength to account for the influence of body height and body weight, the magnitudes of the correlations between bone mineral density and muscle strength diminished substantially and were not significantly different from zero. The results reveal that, for a typical sample of healthy older adults not involved in resistance training, the relationship between maximal isometric muscle strength of lower extremity joints and proximal femur bone mineral density is reliant on body size.