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Introduction: This study performed motor unit number estimation (MUNE) of the abductor hallucis (AH) muscle from 16 healthy control participants on the basis of the compound muscle action potential (CMAP) scan., Methods: Muscle responses to electrical stimuli ranging from subthreshold to supramaximal intensity were recorded, and MUNE was determined from a model of the responses (MScanFit program)., Results: The average CMAP amplitude and MUNE of the AH for the right and left sides combined were 19.6 ± 0.75 mV and 127 ± 5 (mean ± SE), respectively., Discussion: Findings of the study provide useful information about the motor unit number of the AH. Muscle Nerve 58: 735-737, 2018., (© 2018 Wiley Periodicals, Inc.)

Introduction: Excitability properties of motor nerves to different muscles are different, but the explanation is uncertain. We characterized motor axon excitability properties to the medial gastrocnemius (MG) in 27 adults, and made comparisons with the peroneal nerve to the tibialis anterior (TA) and median nerve to the abductor pollicis brevis (APB) in 10 subjects., Methods: Recordings of multiple excitability properties were made using threshold tracking, stimulating the nerves at the wrist or knee., Results: Threshold electrotonus and superexcitability differed between nerves (APB>MG>TA axons) that may reflect differences in fast K + conductance. APB axons had larger S2 accommodation and undershoot than TA and MG axons, indicating greater slow K + conductance. TA axons demonstrated greater accommodation during hyperpolarizing currents than MG and APB axons, suggestive of greater inwardly rectifying current., Discussion: Inherent differences in several conductances underlie nerve differences in excitability, presumably related to muscle or motoneuron properties. Muscle Nerve 57: E60-E69, 2018., (© 2017 Wiley Periodicals, Inc.)

We have compared the number of muscle fibers in the biceps brachii muscle (BB) of six old men (82.3 +/- 4.3 years) and six young men (21.2 +/- 1.9 years). Muscle fiber number was estimated by dividing the maximal area of the BB, determined with magnetic resonance imaging, by the mean fiber area of the BB determined in a muscle biopsy. The percentage of type II fibers in the BB ( approximately 60%) and the type I fiber area were not different between the groups. The BB area (-26%), type II fiber area (-24%), mean fiber area (-20%), and maximal voluntary contraction strength (MVC) of the elbow flexor muscles (-27%) were lower in the old than young group. However, the estimated number of muscle fibers was not significantly different between the young (253000) and old (234000) men. Consequently, the smaller BB area of the old men could be explained primarily by a smaller type II fiber size. These findings suggest that old age is not associated with a reduced number of muscle fibers in the BB. The relative contribution of a reduction in fiber number to age-related muscle atrophy may be muscle-dependent.