Influence of age on passive stiffness and size, quality, and strength characteristics

INTRODUCTION: We examined the effects of aging on passive stiffness, size, quality, and strength characteristics of the posterior hip and thigh muscles. METHODS: Fifteen young (25 ± 3 years) and 15 old (72 ± 5 years) men participated in this study. Echo intensity (EI) and cross-sectional area (CSA) were determined from ultrasound scans of the hamstrings. Straight-leg raises were used to assess passive stiffness, which was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle-torque curve. Peak torque (PT) and rate of torque development (RTD) were assessed through maximal voluntary contractions. RESULTS: Phase 2 slope and EI were higher (P ≤ 0.024), and CSA, PT, and RTD were lower (P ≤ 0.011) in the old compared with the young men; however, no difference (P = 0.145) was observed for phase 1 slope. CONCLUSIONS: Decreases in muscle quality, as indicated by increases in EI, may contribute to the greater passive stiffness observed in older adults. Muscle Nerve 55: 305-315, 2017.