The estimated numbers and relative sizes of thenar motor units as selected by multiple point stimulation in young and older adults

Abstract

Multiple point stimulation (MPS) is described as a method of estimating the numbers of motor units in the median innervated thenar muscles of young and older control subjects. Stimulation at multiple sites along the course of the median nerve was employed to collect a sample of the lowest threshold, all-or-nothing surface-recorded motor unit action potentials (S-MUAPs). The average, negative peak area, and peak-to-peak amplitude of the sample of S-MUAPs was determined and divided into the corresponding value for the maximal compound muscle action potential to derive the motor unit estimate (MUE). In 37 trials from 17 younger subjects (20-40 years), the mean MUE was 288 +/- 95 SD based on negative peak area and, in 33 trials from 20 older subjects, mean values were 139 +/- 68. In 23 young and older subjects, MPS was performed on at least two occasions and the MUEs were found to be highly correlated (r = 0.88).

Assessment of biomarkers of protein anabolism in skeletal muscle during the life span of the rat: sarcopenia despite elevated protein synthesis

“…In addition to a disregulation of hormonal homeostasis, an elevation of inflammatory activity and TNF-␣ signaling (16) has also been suggested to contribute to sarcopenia. Furthermore, in humans and rodents, it has been observed that, with age, neuromuscular communication becomes dysfunctional, spinal cord motor neurons die, and motor units are lost (3,6,19). In rats this has been reported to lead to an increased incidence of denervation (28).…”

Method for Counting Motor Units in Mice and Validation Using a Mathematical Model

“…This overlap results in stimulus-tostimulus alternation of the axons excited with a constant stimulus Milner-Brown and Brown 1976). There is no evidence for a systematic relationship between threshold and motor axon diameter using percutaneous stimuli in human nerves (Doherty and Brown 1993;Doherty and Stashuk 2003). Therefore in the model, axon thresholds were randomly associated with motor unit twitch forces.…”

Test–retest reliability of a modified multiple point stimulation technique for motor unit number estimation

“…Once the lowest threshold SMUPs had been collected, the stimulator was moved approximately 15 mm along the nerve trunk. This distance was so chosen because, beyond that, the risk of inadvertently activating the same SMUPs is negligible (Doherty and Brown, 1993). After all SMUPs were collected (i.e., no additional SMUPs were observed at either stimulus pulse width), the program averaged the SMUPs in a "data point by data point" manner.…”

“…Motor unit number estimation (MUNE) is a neurophysiological method that can help to define the severity, follow the progression and detect the efficacy of treatment of neuromuscular diseases, in which motor neuronal or axonal loss is a major feature (Doherty and Brown, 1993;Simmons et al, 2001). There are a variety of MUNE techniques, most of which derive the estimate of motor units from the ratio of the maximum compound muscle action potential (CMAP) to the average surface motor unit action potential (SMUP).…”

“…In standard MPS, SMUPs are collected along the superficial portion of a nerve using only short pulse width. Doherty and Brown (1993) showed that the mean percentage error of the MUNE could be reduced if more than 10 SMUPs were obtained. In a recent study, we demonstrated that a greater increase in the sample size of SMUPs could be achieved by additionally using a long stimulus pulse width (1 ms) (Porter et al, in press).…”