Title

Age-related changes in passive musculotendinous stiffness and muscle quality of the hamstrings

Document Type

Presentation

Journal/Book Title/Conference

American College of Sports Medicine 2016 National Conference

Publisher

American College of Sports Medicine

Location

Boston, MA

Publication Date

6-3-2016

Abstract

With a rapidly growing elderly population, it is essential to expand our understanding of the age-related changes in musculotendinous stiffness (MTS) characteristics and their underlying mechanisms. Previous studies have reported that decreases in muscle quality [echo intensity (EI)], which are indicative of greater intramuscular fat and fibrous tissue content, may contribute to the lower muscle strength values typically observed in old compared to young adults. However, we are aware of no previous studies that have examined the contribution of muscle quality to age-related changes in MTS. PURPOSE: To determine the effects of aging on MTS and EI of the hamstrings in young and old men. METHODS: Fifteen young (age = 25 ± 3 yr) and 15 old (72 ± 5 yr) men underwent two diagnostic ultrasound assessments followed by two passive straight-leg raises (SLR) using an isokinetic dynamometer programmed in passive mode to move the foot toward the head at 5°·s-1. EI of the semitendinosus was measured on the right leg using a portable B-mode ultrasound imaging device and linear-array probe. For each SLR, participants lied in a supine position with the knee- and ankle-joints immobilized with custom-built stabilizing apparatuses. All assessments were performed on the right leg, while the left thigh and ankle were secured with restraining straps. MTS was calculated during each SLR as the slope of the final 10% of the angle-torque curve. RESULTS: The old men exhibited greater MTS (old = 2.08 ± 0.99 Nm·deg-1; young = 1.46 ± 0.62 Nm·deg-1; P = 0.048) and EI (old = 95.90 ± 10.12 AU; young = 77.60 ± 10.96 AU; P < 0.001) values than the young men. There was a significant relationship between MTS and EI in the old men (r = 0.666; P = 0.007) but not in the young men (r = -0.211; P = 0.451). CONCLUSION: These findings demonstrated that hamstrings passive stiffness increases and muscle quality decreases at old age. The significant relationship observed between MTS and EI in the old men perhaps suggests that these age-related declines in muscle quality may play a significant role in the greater passive stiffness values observed in older adults. As a result, practitioners may consider implementing training programs aimed at decreasing EI of the hamstrings in the elderly which may be beneficial for both improving muscle quality and simultaneously reducing passive stiffness.

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