Determinants of lower-body muscle power in early postmenopausal women

Abstract

OBJECTIVES: To investigate the association between muscle size, density, and fiber composition; body composition; maximal isometric knee extension strength (KES); and lower-body muscle power in healthy postmenopausal women. DESIGN: Cross-sectional analysis of baseline data from a 1-year randomized controlled experiment. SETTING: University-based research laboratory. PARTICIPANTS: Seventy-eight healthy postmenopausal women aged 50 to 57. MEASUREMENTS: Maximal lower-body muscle power was assessed using vertical jump height (VJH). Maximal isometric KES was measured on a dynamometer chair. Computed tomography scans were used to determine lean-tissue cross-sectional area and density of the thigh and lower leg muscles. Relative area occupied by type I, IIa, Ilax, and IIx muscle fibers was assessed from the vastus lateralis muscle. Lean body mass and total body fat mass were assessed using bioelectrical impedance. RESULTS: High VJH was associated with low body fat mass, high KES, and high density of thigh and lower leg muscles. Multivariate linear regression modeling revealed that high thigh muscle density (β = 0.242; P = .019), relative area occupied by the fastest muscle fiber types (IIax + IIx; β = 0.246; P = .007), KES (β = 0.247; P = .007), and low body fat mass (β = -0.455; P < .001) were independently associated with high VJH, accounting for 45% of the variability in VJH. CONCLUSION: This study showed that thigh muscle composition, muscle strength, and body fat mass are important determinants of lower-body muscle power production during weight-bearing activity in healthy postmenopausal women.