Muscular strength measurements indicate bone mineral density loss in postmenopausal women

Zhixiong Zhou,^1,2 Lu Zheng,³ Dengyun Wei,⁴ Ming Ye,³ Xun Li<sup>2

1</sup>School of Physical Education and Coaching Science, Capital University of Physical Education and Sports, Beijing, People’s Republic of China; ²Graduate School, Beijing Sport University, Beijing, People’s Republic of China; ³School of Kinesiology and Health Education, Capital University of Physical Education and Sports, Beijing, People’s Republic of China; ⁴Department of Physical Education, Anhui Normal University, Anhui, People’s Republic of China

Background: The literature is inconsistent and inconclusive on the relationship between bone mineral density (BMD) and muscular strength in postmenopausal women.
Objective: To evaluate the relationship between isokinetically and isometrically determined muscle strength and BMD in postmenopausal women of different age groups.
Methods: Healthy postmenopausal women (n = 293; mean age, 54.22 ± 3.85 years) were enrolled in this study. They were grouped by age according to World Health Organization life expectancy: 45–50 years, 51–53 years, 54–56 years, 57–59 years, and 60–64 years. Total BMD, L2–4 BMD, and femoral neck BMD were measured by dual-energy X-ray bone densitometry; isokinetic and isometric muscle strength of the right hip and trunk muscles were measured during contractile exercise. Stepwise regression analysis was used to examine the relationships between BMD and strength measures, controlling for subject age and years since menopause.
Results: Results of stepwise regression showed that hip extensor and flexor strength at 120°/second and back extend strength at 30°/second accounted for 26% total BMD variance among menopausal subjects, 19% L2–4 BMD variance, and 15% femoral neck BMD variance; in postmenopausal women of different age groups, hip extensor and flexor strength at 120°/second and back extend strength at 30°/second accounted for 25%–35% total BMD variance.
Conclusion: Different optimal strength measurements were identified for different age groups. Age-appropriate testing mode can improve detection of osteoporotic fracture risk in early menopause by determining muscular strength reduction related to BMD loss. This may enable early initiation of preventative therapies.

Keywords: osteoporosis, fracture, bone mineral density, postmenopausal, menopause, muscle strength, isokinetic, isometric