title: Achilles tendon displacement patterns during passive stretch and eccentric loading are altered in middle-aged adults.
abstract: The purpose of this study was to investigate middle-age effects on Achilles displacement patterns under passive stretch and eccentric loading. Healthy young (24.1 ± 1.4 years, n = 9) and middle-aged (49.0 ± 3.1 years, n = 9) adults were positioned prone and the ankle was cyclically dorsiflexed (0.5 Hz, 25° range) during passive stretch and active lengthening. Achilles displacements were tracked in cine ultrasound using 2D speckle tracking. Displacements were found to be non-uniform, with mid and deep portions of the tendon displacing more than superficial portions. However, the degree of non-uniformity was significantly reduced in middle-aged adults, suggesting a potential age-related reduction in inter-fascicle sliding or a shift in loading sharing between plantarflexors. Eccentric loading reduced displacement magnitudes, likely reflecting distal tendon stretch induced via active muscle contractions. Changes in tendon displacement with active loading were greater in middle-aged adults, which could reflect greater tendon compliance. The observed age-related changes in Achilles tendon behavior may have implications for both plantarflexor performance and injury risk.
authors.affiliation: Department of Biomedical Engineering, 1550 Engineering Drive, Madison, WI 53706, United States. Electronic address: laura.c.slane@gmail.com.
authors.forename: Laura Chernak
authors.initials: LC
authors.lastname: Slane
authors.affiliation: Department of Biomedical Engineering, 1550 Engineering Drive, Madison, WI 53706, United States; Department of Mechanical Engineering, 1513 University Ave, Madison, WI 53706, United States; Department of Orthopedics and Rehabilitation, 1300 University Ave, Madison, WI 53706, United States. Electronic address: thelen@engr.wisc.edu.
authors.forename: Darryl G
authors.initials: DG
authors.lastname: Thelen
mesh_terms: D000125:Achilles Tendon / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology*; D000375:Aging / Q000473:pathology / Q000502:physiology*; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009929:Organ Size; D016059:Range of Motion, Articular / Q000502:physiology; D014463:Ultrasonography; D055815:Young Adult
keywords: Non-uniform motion; Ultrasound speckle tracking