Mapping activation levels of skeletal muscle in healthy volunteers: An MRI study

Ryuta Kinugasa*, Yasuo Kawakami, Tetsuo Fukunaga

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


Purpose: To use muscle functional MRI (mfMRI) to compare activation levels within and among triceps surae (TS) muscles. Materials and 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. Conclusion: 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.

Original languageEnglish
Pages (from-to)1420-1425
Number of pages6
JournalJournal of Magnetic Resonance Imaging
Issue number6
Publication statusPublished - 2006 Dec 1


  • 3D
  • Exercise
  • Motor unit
  • T2
  • Triceps surae muscles
  • mfMRI

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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