Corticospinal excitability to the biceps and triceps brachii during forward and backward arm cycling is direction- and phase-dependent

Abstract

The purpose of this study was to evaluate supraspinal and spinal excitability to the biceps and triceps brachii when comparing forward (FWD) and backward (BWD) arm cycling. Supraspinal and spinal excitability were assessed non‐invasively using transcranial magnetic stimulation (TMS) to elicit motor evoked potentials (MEPs) and transmastoid electrical stimulation (TMES) to elicit cervicomedullary evoked potentials (CMEPs), respectively. MEPs and CMEPs were recorded from the biceps and triceps brachii during FWD and BWD arm cycling at two positions, the 6 and 12 o'clock position. The 6 o'clock position corresponded to mid elbow flexion and extension during FWD and BWD cycling, respectively, while the 12 o'clock position corresponded to mid elbow extension and flexion during FWD and BWD cycling, respectively. Participants completed four arm cycling trials, two FWD and two BWD, at 60 rpm and 25 W. During the flexion phase MEP (p = .001) and CMEP (p = .001) amplitudes of the biceps brachii were higher during FWD cycling. However, during the extension phase MEP (p = .006) and CMEP (p = .003) amplitudes were higher during BWD cycling. For the triceps brachii MEP amplitudes were higher during FWD cycling compared to BWD (p = .027) regardless of the functional phase (flexion vs. extension) of the movement cycle. However, spinal excitability to the triceps brachii was dependent on the functional phase of the movement cycle. During the flexion phase CMEPs of the triceps brachii were higher during FWD cycling compared to BWD (p = .032), but during the extension phase CMEPs were higher during BWD cycling compared to FWD (p = .001). This data suggests that the modulation of CSE and spinal excitability to the biceps brachii is dependent on the functional phase of the movement cycle and on the cycling direction. Also, spinal excitability but not CSE to the triceps brachii is dependent on the functional phase of the movement cycle when comparing FWD and BWD cycling. Support or Funding Information NSERC Discovery Grant awarded to K.E. Power This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Changes in muscle activity during the flexion and extension phases of arm cycling as an effect of power output are muscle-specific

“…Cycle crank positions were made relative to a clock face (12, 3, 6, and 9 o’clock, as viewed from the right crank arm) with the “top dead centre” position of the crank arm defined as 12 o’clock and “bottom dead centre” as 6 o’clock, which is identical to previous investigations ( Carroll et al, 2006 ; Klimstra, Thomas & Zehr, 2011 ; Nippard et al, 2020 ; Power et al, 2018 ; Zehr et al, 2004 ; Zehr & Chua, 2000 ). The biceps brachii and triceps brachii were the main muscles of interest, thus the terminology used to describe the cycling movement is based on the position of the dominant elbow joint.…”

Moving forward: methodological considerations for assessing corticospinal excitability during rhythmic motor output in humans

“…Over the past several years, we have investigated the corticospinal control of arm cycling across a variety of conditions using each of the aforementioned methods for setting stimulation parameters (25,26,29,33,59,60,63,(89)(90)(91). For various reasons, we have used different methods to set stimulation intensities across different studies, which has undoubtedly contributed to the existing variability in methods used for setting stimulation parameters across the field of human neurophysiology.…”

Peer Review #1 of "Changes in muscle activity during the flexion and extension phases of arm cycling as an effect of power output are muscle-specific (v0.1)"

“…Participants gripped the ergometer handles with the forearms in a pronated position. Cycle crank positions were made relative to a clock face (12, 3, 6, and 9 o'clock, as viewed from the right crank arm) with the "top dead centre" position of the crank arm defined as 12 o'clock and "bottom dead centre" as 6 o'clock, which is identical to previous investigations (Carroll et al 2006;Klimstra et al 2011;Nippard et al 2020;Power et al 2018;Zehr & Chua 2000). The biceps brachii and triceps brachii were the main muscles of interest, thus the terminology used to describe the cycling movement is based on the position of the dominant elbow joint.…”