Differences in corticospinal excitability to the biceps brachii between arm cycling and tonic contraction are not evident at the immediate onset of movement

Abstract

With the use of indirect stimulation techniques, it is possible to examine the basic, underlying mechanisms involved with the neuronal control of voluntary motor outputs in humans. By developing a better understanding of how the central nervous system functions during these outputs, we allow for the possibility of improving current rehabilitative and therapeutic strategies for people with neurological injuries and/or diseases. Recently, this type of work has demonstrated that corticospinal excitability is not task-dependent prior to the initiation of a motor output. However, substantial evidence has shown that corticospinal excitability is task-dependent during motor outputs. Considering these two findings, it is highly plausible that a transition occurs in corticospinal excitability from task-independent to task-dependent as movement progresses from rest to steady-state. The timeline of this transition is poorly understood.Therefore, the purpose of this study was examine the possible task-dependent transition in corticospinal excitability from rest to steady-state arm cycling.iii ACKNOWLEDGEMENTS

Changes in Corticospinal and Spinal Excitability to the Biceps Brachii with a Neutral vs. Pronated Handgrip Position Differ between Arm Cycling and Tonic Elbow Flexion

“…Vertex was determined by measuring the mid-point between the participant’s nasion and inion, and the mid-point between the participant’s tragi. The intersection of these two points was measured, marked and defined as vertex (Forman et al, 2014, 2015, 2016b; Pearcey et al, 2014; Copithorne et al, 2015; Philpott et al, 2015). The coil was held tangentially to the participant’s skull (approximately parallel to the floor) with the direction of the current flow preferentially activating the left motor cortex.…”

“…Because changes in MEP and CMEP amplitudes can be the result of changes to the Mwave, both MEPs and CMEPs were normalized to the Mwaves evoked during the same experimental condition. Pre-stimulation EMG was measured from rectified traces and was defined as a 50 ms window of the mean rectified EMG immediately prior to the stimulation artifact (Forman et al, 2014, 2015, 2016b). Measurements were taken from the averaged files of all eight MEPs or all eight CMEPs.…”

Phase- and Workload-Dependent Changes in Corticospinal Excitability to the Biceps and Triceps Brachii during Arm Cycling

“…Considerably less information is currently available regarding corticospinal excitability (CSE) modulation during locomotor outputs, though we are beginning to understand CSE modulation during leg [7,12,13] and arm cycling [8,14,15,16]. CSE can be assessed by measuring the amplitude of motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of corticospinal axons.…”

“…CSE can be assessed by measuring the amplitude of motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of corticospinal axons. Together, these measures give an indication of supraspinal and spinal excitability [8,14,16,17,18,19]. Using these techniques, Sidhu and colleagues have recently shown that CSE is phase-, muscle- and intensity-dependent to the leg muscles during cycling [7,12,13].…”

“…Using these techniques, Sidhu and colleagues have recently shown that CSE is phase-, muscle- and intensity-dependent to the leg muscles during cycling [7,12,13]. Work from our lab has shown phase-, task- and cadence-dependent modulation of CSE to the biceps brachii during arm cycling [8,14,15,16]. More specifically, while CSE to the biceps brachii increased throughout arm cycling as cadence increased, spinal excitability increased during elbow flexion and decreased during elbow extension [16].…”