title: Alterations in intramuscular water movement associated with mechanical changes in human skeletal muscle fibers: an evaluation using magnetic resonance diffusion-weighted imaging and B-mode ultrasonography.
abstract: BACKGROUND
  Intramuscular water movement is expected to be affected by the mechanical changes of the muscle fibers. However, the effect of changes in fiber length (FL) and pennation angle (PA) on the water movement has not been sufficiently investigated in human skeletal muscles.
  
  
  OBJECTIVE
  To determine the relationship between intramuscular water movement and the mechanical changes in human muscle fibers.
  
  
  METHODS
  Axial magnetic resonance diffusion-weighted images of the right leg (eight men) were taken using a 1.5-Tesla device with the ankle joint maximally dorsiflexed and maximally plantar flexed. The apparent diffusion coefficient (ADC) values of both the dorsiflexors (the superficial and deep parts of the tibialis anterior) and the plantar flexors (medial gastrocnemius and soleus) were calculated along three orthogonal axes (S-I: superior-to-inferior, A-P: anterior-to-posterior, and R-L: right-to-left). FL and PA of both muscle groups were also calculated from longitudinal B-mode ultrasound images with the ankle joint maximally dorsiflexed and plantar flexed.
  
  
  RESULTS
  There was a significant increase in the ADC in superficial (P < 0.05) and deep (P < 0.05) parts of the dorsiflexors in the S-I direction when the ankle was plantar flexed and in the A-P and R-L directions when the ankle was dorsiflexed (P < 0.05). The plantar flexors showed significantly elevated ADC in the S-I direction when the ankle was dorsiflexed (P < 0.05), and in the A-P and R-L directions when the ankle was plantar flexed (P < 0.05). The dorsiflexors also showed significantly increased PA and decreased FL values when the ankle was dorsiflexed (P < 0.05). The plantar flexors displayed similar morphological changes when the ankle was plantar flexed (P < 0.05).
  
  
  CONCLUSIONS
  Water diffusion is affected by structural changes in the long axis of the muscle fibers, namely the changes in PA and FL.
authors.affiliation: Waseda University, Japan. o.yanagisawa@aoni.waseda.jp
authors.forename: Osamu
authors.initials: O
authors.lastname: Yanagisawa
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kurihara
authors.forename: Toru
authors.initials: T
authors.lastname: Fukubayashi
mesh_terms: D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D038524:Diffusion Magnetic Resonance Imaging; D006801:Humans; D007866:Leg; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000000981:diagnostic imaging* / Q000502:physiology*; D014463:Ultrasonography / Q000379:methods; D014872:Water Movements; D055815:Young Adult