Sex- and age-related declines in muscle mass, strength, physical performance, and muscle quality among community-dwelling older adults: A cross-sectional study

Muscle volume, strength, physical performance, and quality (functional and morphological domains) decline with age; however, the specific patterns and differences among these variables in old age remain unclear. We quantitatively assessed sex- and age-related changes and differences among these variables in older adults. We hypothesized that the rates of age-related decline differ among the parameters. Specifically, muscle quality would decline more steeply than muscle mass, with sex-related variations. A cross-sectional survey of 1370 community-dwelling Japanese older adults (aged 65-90 years) was conducted. Muscle mass and volume were measured by appendicular lean mass (ALM) index using bioelectrical impedance spectroscopy (BIS) and thigh muscle thickness (MT) using ultrasonography. Physical performance was assessed by the 5-times chair stand, timed up-and-go test, maximum walking speed, and vertical jump × body weight. Handgrip strength (HG) and knee extension strength (KES) were used to assess muscle strength. Functional (HG/ALM and KES/MT) and morphological (whole-body and thigh phase angles [PhA], extracellular/intracellular water ratio [ECW/ICW] by BIS, and thigh echo intensity by ultrasonography) domain muscle qualities were assessed. Linear regression predicted significant age-related declines in all parameters. The predicted decline rates/year were as follows: thigh MT (male: 0.9 %; female: 1.1 %), KES (male: 2.0 %; female: 2.1 %), lower extremity physical performance (male: 1.4-2.8 %; female: 1.8-3.0 %), thigh morphological muscle quality via BIS (male: 1.5-2.2 %; female: 1.4-1.9 %), echo intensity (male: 1.2 %; female: 0.5 %), and functional muscle quality (KES/MT) (male: 1.3 %; female: 1.3 %). The slopes of lower extremity strength, performance, and muscle quality were steeper than those of muscle mass. These patterns also varied by parameter and sex. This study provides novel insight into the differential aging patterns of muscle mass, strength, performance, and functional (e.g., KES/MT) and morphological (e.g., PhA, ECW/ICW, EI) muscle quality by simultaneously comparing age- and sex-related changes in these parameters. Our findings highlight muscle quality, particularly in the lower limbs, as a sensitive and distinct indicator of age-related physical decline. These findings offer new perspectives for assessing and intervening with older adults.