Department of Human Science, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama, Kanagawa 221-8686, Japan.
Exp Physiol. 2011 Sep;96(9):938-48. doi: 10.1113/expphysiol.2011.057562. Epub 2011 Jun 10.
The present study examined spatial changes in the muscle activation pattern with different contraction intensity using magnetic resonance imaging (MRI). Transverse relaxation time (T2)-weighted MRI was used to acquire 22 axial slices, which covered the entire medial gastrocnemius muscle, before and immediately after seven sets of 10 plantarflexions with loads that were approximately 20 and 60% of their one-repetition maximum, respectively. Reconstructions of the activated regions from MR images revealed the following: (1) the muscle activation determined by MRI correlated significantly (P < 0.05) with the results of electromyography; (2) the activated area distribution increased with increasing force levels; and (3) differential activation between 20 and 60% load was distributed in a spatially non-uniform manner within the muscle, and some regions indicated reduced activity. These results indicate that at submaximal contraction intensity, activation does not necessarily increase in the whole muscle with increase in contraction intensity.
本研究使用磁共振成像（MRI）检查了不同收缩强度下肌肉激活模式的空间变化。在进行七组分别约为 20%和 60%最大重复次数的 10 次跖屈运动前和运动后立即，使用 T2 加权 MRI 采集了覆盖整个内侧腓肠肌的 22 个轴向切片。从 MRI 图像重建的激活区域显示：（1）MRI 确定的肌肉激活与肌电图结果显著相关（P < 0.05）；（2）激活区域分布随力水平的增加而增加；（3）20%和 60%负荷之间的差异激活在肌肉内呈空间不均匀分布，一些区域显示活性降低。这些结果表明，在次最大收缩强度下，激活不一定随收缩强度的增加而在整个肌肉中增加。
