Background: We examined corticospinal and spinal excitability across multiple power outputs during arm cycling using a weak and strong stimulus intensity. Methods: We elicited motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs) in the biceps brachii using magnetic stimulation over the motor cortex and electrical stimulation of corticospinal axons during arm cycling at six different power outputs (i.e., 25, 50, 100, 150, 200 and 250 W) and two stimulation intensities (i.e., weak vs. strong). Results: In general, biceps brachii MEP and CMEP amplitudes (normalized to maximal M-wave (Mmax)) followed a similar pattern of modulation with increases in cycling intensity at both stimulation strengths. Specifically, MEP and CMEP amplitudes increased up until ~150 W and ~100 W when the weak and strong stimulations were used, respectively. Further increases in cycling intensity revealed no changes on MEP or CMEP amplitudes for either stimulation strength. Conclusions: In general, MEPs and CMEPs changed in a similar manner, suggesting that increases and subsequent plateaus in overall excitability are likely mediated by spinal factors. Interestingly, however, MEP amplitudes were disproportionately larger than CMEP amplitudes as power output increased, despite being initially matched in amplitude, particularly with strong stimulation. This suggests that supraspinal excitability is enhanced to a larger degree than spinal excitability as the power output of arm cycling increases.

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.

Background: The present study compared corticospinal excitability to the biceps brachii muscle during arm cycling at a self-selected and a fixed cadence (SSC and FC, respectively). We hypothesized that corticospinal excitability would not be different between the two conditions. Methods: The SSC was initially performed and the cycling cadence was recorded every 5 seconds for one minute. The average cadence of the SSC cycling trial was then used as a target or FC of cycling that the participants were instructed to maintain. Motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation (TMS) of the motor cortex were recorded from the biceps brachii during each trial of SSC and FC arm cycling. Results: Corticospinal excitability as assessed via normalized MEP amplitudes (MEPs were made relative to a maximal compound muscle action potential) were not different between groups. Conclusions: Focusing on maintaining a FC cadence during arm cycling does not influence corticospinal excitability as assessed via TMS-evoked MEPs.

Background: The present study compared corticospinal excitability to the biceps brachii muscle during arm cycling at a self-selected and a fixed cadence (SSC and FC, respectively). We hypothesized that corticospinal excitability would not be different between the two conditions. Methods: The SSC was initially performed and the cycling cadence was recorded every 5 s for one minute. The average cadence of the SSC cycling trial was then used as a target for the FC of cycling that the participants were instructed to maintain. The motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation (TMS) of the motor cortex were recorded from the biceps brachii during each trial of SSC and FC arm cycling. Results: Corticospinal excitability, as assessed via normalized MEP amplitudes (MEPs were made relative to a maximal compound muscle action potential), was not different between groups. Conclusions: Focusing on maintaining a fixed cadence during arm cycling does not influence corticospinal excitability, as assessed via TMS-evoked MEPs.

Background: The present study compared corticospinal excitability to the biceps brachii muscle during arm cycling at a self-selected and a fixed cadence (SSC and FC, respectively). We hypothesized that corticospinal excitability would not be different between the two conditions. Methods: The SSC was initially performed and the cycling cadence was recorded every 5 seconds for one minute. The average cadence of the SSC cycling trial was then used as a target for FC of cycling that the participants were instructed to maintain. Motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation (TMS) of the motor cortex were recorded from the biceps brachii during each trial of SSC and FC arm cycling. Results: Corticospinal excitability as assessed via normalized MEP amplitudes (MEPs were made relative to a maximal compound muscle action potential) were not different between groups. Conclusions: Focusing on maintaining a FC cadence during arm cycling does not influence corticospinal excitability as assessed via TMS-evoked MEPs.