Chapter 1 Motor unit number estimations (MUNEs): past, present and future

Publisher This chapter provides an overview on the physiological technique for estimating the number of motor units (MUs) in the extensor digitorum brevis (EDB) muscle. The average size of the first several surface-detected motor unit potentials (S-MUAPs) associated with electrical stimulation of their associated motor nerve fibers (MNFs). It discusses that an estimate of the number of EDB MUs was derived by division of the negative peak amplitude of the maximum ‘M,’ potentially evoked by supramaximal stimulation of the same peroneal nerve at the same site by the negative amplitude of the average S-MUAP. The chapter also reviews that to stimulate the nerve at several points along its course at each site, accepting only those lowest threshold MNFs and their associated S-MUAPs whose thresholds did not overlap, and adding them to the sample of S-MUAPs used to calculate the average S-MUAP size. This technique is known as multiple point stimulation (MPS). The chapter concludes that there are certain issues surrounding MPS that needs to be discussed further, because the method of stimulating single MNFs underpins later studies and proposals for longitudinal studies of single MUs.