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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\u2014tendon 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.<\/jats:p>","DOI":"10.1038\/s41598-022-05795-7","type":"journal-article","created":{"date-parts":[[2022,2,1]],"date-time":"2022-02-01T11:03:48Z","timestamp":1643713428000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":19,"title":["Mechanical properties of muscles and tendon structures in middle-aged and young men"],"prefix":"10.1038","volume":"12","author":[{"given":"Keitaro","family":"Kubo","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Toshihiro","family":"Ikebukuro","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hideaki","family":"Yata","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2022,2,1]]},"reference":[{"key":"5795_CR1","doi-asserted-by":"publisher","first-page":"1199","DOI":"10.1097\/00005768-200207000-00023","volume":"34","author":"SJ Pearson","year":"2002","unstructured":"Pearson, S. 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