Fig. 2.

Signal intensity in a motor unit over time during the fine-grain experiment revealing the phenomena of alternation. If the current strength is slowly increased, at a certain current the signal intensity drops followed by a period where the signal intensity is alternatingly high or low (motor unit alternation), until the current reaches a level that the signal intensity remains low (continuously active motor unit). Panel of images correspond to different points during the period of alternation, showing an alternating unit indicated by the red arrows.