Evidence for intermuscle difference in slack angle in human triceps surae

Kosuke Hirata, Hiroaki Kanehisa, Eri Miyamoto-Mikami, Naokazu Miyamoto*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

55 Citations (Scopus)


This study examined whether the slack angle (i.e., the joint angle corresponding to the slack length) varies among the synergists of the human triceps surae in vivo. By using ultrasound shear wave elastography, shear modulus of each muscle of the triceps surae was measured during passive stretching from 50° of plantar flexion in the knee extended position at an angular velocity of 1°/s in 9 healthy adult subjects. The slack angle of each muscle was determined from the ankle joint angle-shear modulus relationship as the first increase in shear modulus. The slack angle was significantly greater in the medial gastrocnemius (20.7±6.7° plantarflexed position) than in the lateral gastrocnemius (14.9±6.7° plantarflexed position) and soleus (2.0±4.8° dorsiflexed position) and greater in the lateral gastrocnemius than in the soleus. This study provided evidence that the slack angle differs among the triceps surae; the medial gastrocnemius produced passive force at the most plantarflexed position while the slack angle of the soleus was the most dorsiflexed position.

Original languageEnglish
Pages (from-to)1210-1213
Number of pages4
JournalJournal of Biomechanics
Issue number6
Publication statusPublished - 2015 Apr 13
Externally publishedYes


  • Ankle joint
  • Gastrocnemius
  • Passive force
  • Shear wave elastography
  • Soleus

ASJC Scopus subject areas

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


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