Force-frequency relationships of the three motor unit types in control and trained animals.

<p>Fast fatigable (FF) motor units (MUs) are presented in panel A, fast fatigue resistant (FR) MUs in panel B, and slow (S) MUs in panel C. The control (C) group is represented by open circles, the group trained for 2 weeks (2W) is represented by filled triangles, the group trained for 4 weeks (4W) is represented by filled squares, and the group trained for 8 weeks (8W) is represented by filled diamonds. The dashed horizontal lines in panels A–C indicate the level of 60% of the maximum force (normalized to the maximum tetanus force obtained at 150 Hz) (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195704#pone.0195704.s007" target="_blank">S6 File</a>).