title: The contraction-induced increase in Achilles tendon moment arm: a three-dimensional study.
abstract: The present study aimed to re-examine the influence of the isometric plantarflexors contraction on the Achilles tendon moment arm (ATMA) and the factors influencing the ATMA in three-dimensions. A series of coronal magnetic resonance images of the right ankle were recorded at foot positions of 10° of dorsiflexion, neutral position, and 10° of plantarflexion for the rest condition and the plantarflexors contraction condition at 30% maximal voluntary effort. The shortest distance between the talocrural joint axis and the line of action of the Achilles tendon force projected to the orthogonal plane of the talocrural joint axis was determined as the ATMA. The ATMA determined in the contraction condition was significantly greater by 8mm than that determined in the rest condition. The talocrural joint axis was displaced anteriorly by 3mm and distally by 2mm due to the muscle contraction. As the same time, the line of action of the Achilles tendon force was displaced posteriorly by 5mm and medially by 2mm. These linear displacements of the talocrural joint axis and the line of action of the Achilles tendon force accounted for the difference in the ATMAs between the two conditions by 35.9 and 62.4%, respectively. These angular displacements accounted for the total of 0.4% increase in the ATMA. These results confirm the previous findings reported in two-dimensional studies and found that the linear displacement of the line of action of the Achilles tendon force is the primary source of the contraction-induced increase in the ATMA.
authors.affiliation: Graduate School of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa-shi, Saitama 359-1192, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Hashizume
authors.affiliation: Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa-shi, Saitama 359-1192, Japan.
authors.forename: Soichiro
authors.initials: S
authors.lastname: Iwanuma
authors.affiliation: College of System Engineering and Science, Shibaura Institute of Technology, 307 Fukasaku, Minuma-ku, Saitama-shi, Saitama 337-0003, Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Akagi
authors.affiliation: National Institute of Fitness and Sports in KANOYA, 1 Shiromizu-cho, Kanoya-shi, Kagoshima 891-2393, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kanehisa
authors.affiliation: Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa-shi, Saitama 359-1192, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kawakami
authors.affiliation: Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa-shi, Saitama 359-1192, Japan. Electronic address: tyanai@waseda.jp.
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Yanai
mesh_terms: D000125:Achilles Tendon / Q000502:physiology*; D000328:Adult; D000843:Ankle Joint / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D055815:Young Adult
keywords: Finite helical axis; Muscle contraction; Musculoskeletal model; Talocrural joint; Triceps surae