LAUSR

The motor unit is the basic organizational and functional element for neuromuscular control. In motor neuron diseases, such as amyotrophic lateral sclerosis and spinal muscular atrophy, motor neurons progressively degenerate, resulting in a reduced number of motor units. Loss of motor units is also a major factor in development of sarcopenia (Gilmore et al., 2017). Although motor unit loss can be partially compensated by axonal branching and muscle fiber reinnervation, such compensation becomes insufficient with disease progression. As a result, patients suffer from progressive muscle weakness and loss of function. The number of motor units provides an important biomarker for diagnosing neuromuscular disease, tracking disease progression, and evaluating the effect of treatments and therapies (Olney and Lomen-Hoerth, 2000; Cudkowicz et al., 2006; Neuwirth et al., 2015). This has led to significant efforts in the past 50 years towardmotor unit number estimation (MUNE).