Common input to different regions of biceps brachii long head

Abstract

The purpose of the experiment was to compare the level of synchronization exhibited by pairs of motor units located within and between functionally distinct regions of the biceps brachii muscle. Pairs of single motor units were recorded from seven subjects using separate electrodes located in the lateral and medial aspects of the long head of biceps brachii. Participants were required to exert a combination of flexion and supination torques so that both motor units discharged at approximately 10 pps for >/=200 s and the level of motor unit synchronization could be quantified. When motor unit recordings were sufficiently stable at the completion of this synchrony task, a series of ramp contractions with multiple combinations of flexion and supination torques were performed to characterize the recruitment thresholds of the motor units. Common input strength (CIS) was significantly greater (P < 0.01) for the within-region pairs of motor units (0.28 extra sync. imps/s, n = 26) than for the between-region pairs (0.13 extra sync. imps/s, n = 18), but did not differ significantly for the 12 within-region pairs from the lateral head and 14 from the medial head (0.27 vs. 0.29 extra sync. imps/s; P = 0.83). Recruitment thresholds were measured for 33 motor units, but there was only a weak association between CIS and the respective recruitment patterns for motor unit pairs (n = 9). The present investigation provides evidence of a differential distribution of synaptic input across the biceps brachii motor neuron pool, but this appears to have minimal association with the recruitment patterns for individual motor units.

Identification of regional activation by factorization of high-density surface EMG signals: A comparison of Principal Component Analysis and Non-negative Matrix factorization

“…Several mechanisms may contribute to regional differences in neural drive. In the biceps brachii, short-term synchronization of motor units was reported to be higher for motor units located within the same regions than in different compartments of the muscle (Barry et al, 2009). Similarly, recent evidence suggests that common drive may be higher for motor units identified in the same than in different VM regions (Cabral et al, 2017).…”

Synchronization of low- and high-threshold motor units

“…However, due mostly to technical limitations, the high‐threshold and high‐force producing motor units have been largely neglected in the synchronization literature. Many studies have relied on use of indwelling electrodes for recording of 2 separate single‐motor unit action potential trains . As a result, most studies have been restricted to very low force levels that correspond to less than 10% of a subject's maximum voluntary contraction (MVC) .…”

“…Many studies have relied on use of indwelling electrodes for recording of 2 separate single‐motor unit action potential trains . As a result, most studies have been restricted to very low force levels that correspond to less than 10% of a subject's maximum voluntary contraction (MVC) . Although a few studies have attempted to compare the degree of motor unit synchronization of low‐threshold pairs versus high‐threshold pairs, there remains uncertainty in their findings, since all of these studies limited their subjects to very low force levels.…”

More Variability in Tibialis Anterior Function during the Adduction of the Foot than Dorsiflexion of the Ankle

“…As a consequence of these differences in anatomy, each planar action about a joint involves different sets of muscles and requires unique distributions of synaptic input to the involved pools of motor neurons (1)(2)(3). Moreover, the activation of a muscle to exert a torque in a prescribed direction will require the engagement of other muscles and the modulation of reflex pathways to counteract the unwanted actions of the activated muscle in its other directions (4)(5)(6).…”