title: Contributions of biarticular myogenic components to the limitation of the range of motion after immobilization of rat knee joint.
abstract: BACKGROUND
  Muscle atrophy caused by immobilization in the shortened position is characterized by a decrease in the size or cross-sectional area (CSA) of myofibers and decreased muscle length. Few studies have addressed the relationship between limitation of the range of motion (ROM) and the changes in CSA specifically in biarticular muscles after atrophy because of immobilization. We aimed to determine the contribution of 2 distinct muscle groups, the biarticular muscles of the post thigh (PT) and those of the post leg (PL), to the limitation of ROM as well as changes in the myofiber CSAs after joint immobilization surgery.
  
  
  METHODS
  Male Wistar rats (n = 40) were randomly divided into experimental and control groups. In the experimental group, the left knee was surgically immobilized by external fixation for 1, 2, 4, 8, or 16 weeks (n = 5 each) and sham surgery was performed on the right knee. The rats in the control groups (n = 3 per time point) did not undergo surgery. After the indicated immobilization periods, myotomy of the PT or PL biarticular muscles was performed and the ROM was measured. The hamstrings and gastrocnemius muscles from the animals operated for 1 or 16 weeks were subjected to morphological analysis.
  
  
  RESULTS
  In immobilized knees, the relative contribution of the PT biarticular myogenic components to the total restriction reached 80% throughout the first 4 weeks and decreased thereafter. The relative contribution of the PL biarticular myogenic components remained <20% throughout the immobilization period. The ratio of the myofiber CSA of the immobilized to that of the sham-operated knees was significantly lower at 16 weeks after surgery than at 1 week after surgery only in the hamstrings.
  
  
  CONCLUSIONS
  The relative contribution of the PT and PL components to myogenic contracture did not significantly change during the experimental period. However, the ratio of hamstrings CSAs to the sham side was larger than the ratio of medial gastrocnemius CSAs to the sham side after complete atrophy because of immobilization.
authors.forename: Momoko
authors.initials: M
authors.lastname: Nagai
authors.forename: Tomoki
authors.initials: T
authors.lastname: Aoyama
authors.forename: Akira
authors.initials: A
authors.lastname: Ito
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Iijima
authors.forename: Shoki
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Junichi
authors.initials: J
authors.lastname: Tajino
authors.forename: Xiangkai
authors.initials: X
authors.lastname: Zhang
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Akiyama
authors.affiliation: Department of Motor Function Analysis, Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Shogoin, Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan. kuroki.hiroshi.6s@kyoto-u.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kuroki
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003286:Contracture / Q000473:pathology / Q000503:physiopathology*; D004195:Disease Models, Animal; D006614:Hindlimb; D007103:Immobilization; D007596:Joints / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000473:pathology / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000473:pathology / Q000503:physiopathology*; D016059:Range of Motion, Articular; D017208:Rats, Wistar; D013997:Time Factors