Motor unit number estimation by spatial-temporal summation of single motor unit potentials

Current techniques for motor unit number estimation (MUNE) rely on the amplitude of the compound muscle action potential (CMAP) evoked by supramaximal stimulation and mean amplitude of single motor unit potentials (SMUPs). The phase cancellation during summation is not considered. We developed a technique to address this issue. Slow and fast types of motor unit potentials were collected from 5 normal subjects from their abductor pollicis brevis muscles by low-level voluntary contractions, and near-threshold nerve stimulation, respectively. Two of each type of SMUPs were used as templates for reconstructing the best fitted CMAP using a feed-forward neural network. The total number of SMUPs simulated from the four templates during the reconstruction served as MUNE. The mean MUNE was 222 +/- 98. The technique is simple and noninvasive, and may be applied in the future for MUNE in patients.