Triceps surae muscle-tendon unit length changes as a function of ankle joint angles and contraction levels: The effect of foot arch deformation

Soichiro Iwanuma, Ryota Akagi, Satoru Hashizume, Hiroaki Kanehisa, Toshimasa Yanai, Yasuo Kawakami

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The purpose of this study was to clarify how foot deformation affects the relationship between triceps surae muscle-tendon unit (MTU) length and ankle joint angle. For six women and six men a series of sagittal magnetic resonance (MR) images of the right foot were taken, and changes in MTU length (the displacement of the calcaneal tuberosity), foot arch angle, and ankle joint angle were measured. In the passive session, each subject's ankle joint was secured at 10° dorsiflexed position, neutral position (NP), and 10° and 20° plantar flexed positions while MR images were acquired. In the active session, each subject was requested to perform submaximal isometric plantar flexions (30%, 60%, and 80% of voluntary maximum) at NP. The changes in MTU length in each trial were estimated by two different formulae reported previously. The changes of the measured MTU length as a function of ankle joint angles observed in all trials of the active session were significantly (p<0.05) larger than corresponding values in the passive session and by the estimation formulae. In the passive session, MTU length changes were significantly smaller than the estimated values when the ankle was plantar flexed. The foot arch angle increased as the contraction level increased from rest (117±4°) to 80% (125±3°), and decreased as the ankle was positioned further into plantar flexion in the passive session (115±3°). These results indicate that foot deformation profoundly affects the triceps surae MTU length-ankle joint angle relationship during plantar flexion.

Original languageEnglish
Pages (from-to)2579-2583
Number of pages5
JournalJournal of Biomechanics
Issue number14
Publication statusPublished - 2011 Sep 23



  • Displacement of the calcaneal tuberosity
  • In vivo
  • MRI

ASJC Scopus subject areas

  • Biophysics
  • Orthopedics and Sports Medicine
  • Biomedical Engineering
  • Rehabilitation

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