Figure 2. Example of extension ramp contractions by thumb and index finger while recording from ED5.

From top to bottom: superimposed action potentials from the single motor unit of interest (test motor unit); the intramuscular EMG recording (iEMG); the instantaneous firing frequency of the test unit (firing freq.); little finger force; index finger force; and thumb force. All forces are shown as a percentage of maximal voluntary contraction force (% MVC). In this example, a weak control extension force produced by the little finger was followed by three ramps of increasing force produced by extension of the thumb up to 50% MVC, a control little-finger contraction, and three ramps performed by the index finger. Finally, there is another control extension contraction of the little finger. The test unit was recruited as expected by weak extension contractions of the little finger, but it was also recruited during extension contractions of the thumb.