Abstract
The purpose of this study was to compare the mechanical properties of muscles and tendon structures for plantar flexor muscles at various strain rates and jump performances using single joint between middle-aged and young men in order to clarify the mechanisms of age-related decline in power output during vertical jump of middle-aged people previously reported. Passive muscle stiffness of the medial gastrocnemius muscle was determined based on passive muscle force and fascicle length during passive stretching at four angular velocities. Active muscle stiffness was calculated based on changes in muscle force and fascicle length during stretching at five angular velocities after submaximal isometric contractions. Maximal elongation and hysteresis of tendon structures were assessed from estimated muscle force—tendon elongation during ramp and ballistic contractions. Two kinds of unilateral jump heights using only ankle joint (no-countermovement and countermovement jumps) were measured. No significant differences in passive and active muscle stiffness, tendon structure properties (except for maximal elongation during ramp contraction), or jump heights were found between middle-aged and young men. The results suggest that the mechanical properties of muscles and tendon structures for plantar flexor muscles and jump performances using only ankle joint do not show age-related changes in middle-aged men.
Highlights
The purpose of this study was to compare the mechanical properties of muscles and tendon structures for plantar flexor muscles at various strain rates and jump performances using single joint between middle-aged and young men in order to clarify the mechanisms of age-related decline in power output during vertical jump of middle-aged people previously reported
No significant differences were observed in the muscle thickness of MG (p = 0.512, d = 0.217), lateral gastrocnemius muscle (LG) (p = 0.836, d = 0.067), or soleus muscle (SOL) (p = 0.961, d = 0.015) between middle-aged and young men
The changes in passive torque, fascicle length, and passive muscle stiffness were measured during slow passive stretching at four different angular velocities (5, 15, 30, and 60 deg s−1)
Summary
The purpose of this study was to compare the mechanical properties of muscles and tendon structures for plantar flexor muscles at various strain rates and jump performances using single joint between middle-aged and young men in order to clarify the mechanisms of age-related decline in power output during vertical jump of middle-aged people previously reported. No significant differences in passive and active muscle stiffness, tendon structure properties (except for maximal elongation during ramp contraction), or jump heights were found between middle-aged and young men. Few studies have shown age-related changes in tendon hysteresis[8,10], tendon hysteresis as well as tendon stiffness affect performance during stretch–shortening cycle exercises[13,14] In these studies, the mechanical properties of tendons were investigated during ramp isometric contraction with a low strain rate (2–7 mm s−113,15), and the strain rate of tendons during measurements was markedly lower than that during running and jumping (60–200 mm s−116,17). Length changes in muscle fibers need to be directly determined to assess passive muscle properties, because changes in the joint angle do not necessarily correspond to those in the muscle fiber length
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