Mapping activation levels of skeletal muscle in healthy volunteers: an MRI study.
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.
Kinugasa
Ryuta
R
Research Center of Sports Sciences, Musashino University, Nishitokyo, Tokyo, Japan. kinugasa@musashino-u.ac.jp
Kawakami
Yasuo
Y
Fukunaga
Tetsuo
T
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