Fat mass rather than muscle strength is the major determinant of physical function and disability in postmenopausal women younger than 75 years of age.

Objective: Few studies have investigated the relationships between body composition, functional ability, and age-related disability in postmenopausal women. We investigated the relative role of fat mass, lean mass, and muscle strength in the development of disability in a group of healthy postmenopausal women younger than 75 years.

Design: We performed a cross-sectional study among 396 independently living women aged 56-73 years, randomly selected between 8 and 30 years after menopause. Lean mass and fat mass were assessed by dual-energy x-ray absorptiometry. Muscle strength (grip and leg extensors) was assessed using dynamometry. Functional ability was estimated by Physical Performance Score, physical activity during the preceding year, and impairment in activities of daily living.

Results: Of the participants, 43.7 % were overweight (25 > or = BMI < 30 kg/m2), and 17.7% were obese (BM I > or = 30 kg/m2). Higher muscle strength was observed with increasing lean body mass, and participants with higher muscle strength scored better in the physical performance score and activities of daily living. Higher fat mass was significantly associated with a lower physical performance score, lower physical activity, and a higher frequency of disability. Increasing fat mass was associated with increasing lean mass and decreasing lean/fat ratio. The increase in lean mass and muscle strength associated with higher fat mass was mainly localized in the legs.

Conclusions: Our results support the role of fat mass as the primary risk marker for disability, which might later accelerate by the age-related decrease in lean mass and the development of sarcopenia after the age of 75 years.