title: Mapping activation levels of skeletal muscle in healthy volunteers: an MRI study.
abstract: OBJECTIVE
  To use muscle functional MRI (mfMRI) to compare activation levels within and among triceps surae (TS) muscles.
  
  
  METHODS
  Seven healthy males performed five sets of 10 repetitions of a unilateral heel-raise exercise. T2-weighted images were obtained before and immediately after the exercise. Pixels that showed T2 greater than the mean +1 SD of the region of interest (ROI) in pre-exercise images and lower than the mean +1 SD of the ROI in post-exercise images were identified. The remaining T2 values in the post-exercise images were assigned to five categories indicated by color: red (highest level of activation), yellow, green, sky blue, and blue (lowest level of activation). The images were then used to construct three-dimensional (3D) images from which the volumes at each level of activation were determined.
  
  
  RESULTS
  Within each of the TS muscles the % activated volumes with low and moderate levels of activation were larger than those with a high level of activation (P < 0.05). The % activated volumes with a high level of activation were larger in the medial gastrocnemius than the soleus (Sol; P < 0.05). The Sol had a larger % activated volume with a low level of activation than the lateral gastrocnemius (P < 0.05). Each activation level was nonuniformly distributed along the length within each TS muscle.
  
  
  CONCLUSIONS
  There is substantial variation in the level of activation within and among the TS muscles; however, the activation level is mainly in the moderate to low range in all three muscles.
authors.affiliation: Research Center of Sports Sciences, Musashino University, Nishitokyo, Tokyo, Japan. kinugasa@musashino-u.ac.jp
authors.forename: Ryuta
authors.initials: R
authors.lastname: Kinugasa
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kawakami
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukunaga
mesh_terms: D000328:Adult; D019412:Anatomy, Cross-Sectional / Q000379:methods*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity