title: Evidence for intermuscle difference in slack angle in human triceps surae.
abstract: 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.
authors: National Institute of Fitness and Sports in Kanoya, Kanoya, Kagoshima, Japan.
authors: Kosuke
authors: K
authors: Hirata
authors: National Institute of Fitness and Sports in Kanoya, Kanoya, Kagoshima, Japan.
authors: Hiroaki
authors: H
authors: Kanehisa
authors: Japan Society for the Promotion of Science, Tokyo, Japan.
authors: Eri
authors: E
authors: Miyamoto-Mikami
authors: National Institute of Fitness and Sports in Kanoya, Kanoya, Kagoshima, Japan. Electronic address: miyamoto@nifs-k.jp.
authors: Naokazu
authors: N
authors: Miyamoto
mesh_terms: D000843:Ankle Joint / Q000502:physiology; D054459:Elasticity Imaging Techniques; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D009126:Muscle Relaxation; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D055815:Young Adult
keywords: Ankle joint; Gastrocnemius; Passive force; Shear wave elastography; Soleus