title: Influence of age on passive stiffness and size, quality, and strength characteristics.
abstract: We examined the effects of aging on passive stiffness, size, quality, and strength characteristics of the posterior hip and thigh muscles.
  
  
  
  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.
  
  
  
  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.
  
  
  
  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.
authors.affiliation: Department of Kinesiology and Sport Management, Texas Tech University, Lubbock, Texas, USA.
authors.forename: Ty B
authors.initials: TB
authors.lastname: Palmer
authors.affiliation: Department of Kinesiology and Health Science, Utah State University, Logan, Utah, USA.
authors.forename: Brennan J
authors.initials: BJ
authors.lastname: Thompson
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D013223:Statistics as Topic; D016750:Stiff-Person Syndrome / Q000000981:diagnostic imaging / Q000473:pathology*; D019415:Torque; D014463:Ultrasonography; D055815:Young Adult
keywords: echo intensity; falls risk; hamstrings; range of motion; straight-leg raise; ultrasound