Evan James Lockyer

Previous studies have shown that supraspinal excitability is higher during arm cycling than a position- and intensity-matched tonic contraction, but the underlying mechanisms remain unclear. This study aimed to determine whether long-interval intracortical inhibition (LICI) occurs during arm cycling and if LICI differs between arm cycling and tonic contraction. A paired-pulse transcranial magnetic stimulation (TMS) protocol assessed LICI using a supramaximal conditioning pulse that produced a silent period of approximately 150 ms, followed by a test pulse with a 100 ms interstimulus interval. Stimulation occurred at the 4 o'clock position to align the test pulse with the ascending limb of the biceps brachii electromyography profile during the elbow flexion phase. Additionally, a single-pulse TMS stimulation was delivered 100 ms after the 4 o'clock position. Motor-evoked potentials (MEPs) were measured as ratios: a position-matched ratio of test pulse-evoked MEP over single pulse-evoked MEP. MEP ratios were analyzed for peak-to-peak amplitude during arm cycling and tonic contraction. Results showed that LICI was present during arm cycling ( t(13) = 3.5, p < 0.001, 95% CI [−3.2, −0.75]), but no significant difference in LICI was found between arm cycling and tonic contraction ( t(13) = 1.3, p = 0.242, 95% CI [−0.23, −0.06]). These findings suggest that while LICI is present during arm cycling, it is not task-dependent.

Neuromechanical Differences between Pronated and Supinated Forearm Positions during Upper-Body Wingate Tests

Repeated sprint exercise (RSE) is often used to induce neuromuscular fatigue (NMF). It is currently not known whether NMF is influenced by different forearm positions during arm cycling RSE. The purpose of this study was to investigate the effects of a pronated versus supinated forearm position on elbow flexor NMF during arm cycling RSE. Participants (n = 12) completed ten 10-s maximal arm cycling sprints interspersed by 60 s of rest on 2 separate days using either a pronated or supinated forearm position. All sprints were performed on an arm cycle ergometer in a reverse direction. Prior to and following RSE, NMF measurements (i.e., maximal voluntary contraction (MVC), potentiated twitch (PT), electromyography median frequencies) were recorded. Sprint performance measures, ratings of perceived exertion (RPE) and pain were also recorded. Irrespective of forearm position, sprint performance decreased as sprint number increased. These decreases were accompanied by significant increases in RPE (p < 0.001, ηp² = 0.869) and pain (p < 0.001, ηp² = 0.745). Participants produced greater power output during pronated compared with supinated sprinting (p < 0.001, ηp² = 0.728). At post-sprinting, the percentage decrease in elbow flexor MVC and PT force from pre-sprinting was significantly greater following supinated than pronated sprinting (p < 0.001), suggesting greater peripheral fatigue occurred in this position. The data suggest that supinated arm cycling RSE results in inferior performance and greater NMF compared with pronated arm cycling RSE. Novelty: NMF of the elbow flexors is influenced by forearm position during arm cycling RSE. Supinated arm cycling sprints resulted in worse repeated sprint performance and also greater NMF than pronated RSE.

This is the first demonstration of interhemispheric inhibition (IHI) during a locomotor output, arm cycling. IHI was quantified by assessing the depth of the ipsilateral silent period (iSP) evoked via transcranial magnetic stimulation of the motor cortex. There was a significant reduction in electromyography (EMG) amplitude of the iSP during cycling compared with the control EMG (16.8% ± 17.1%; p < 0.001). Depth and area for measuring the iSP during arm cycling are discussed. Novelty: This is the first study to demonstrate activation of the cortical circuit, interhemispheric inhibition, during a locomotor output.

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.

This is the first study to examine corticospinal excitability (CSE) to antagonistic muscle groups during arm cycling. Transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of the corticospinal tract were used to assess changes in supraspinal and spinal excitability, respectively. TMS induced motor evoked potentials (MEPs) and TMES induced cervicomedullary evoked potentials (CMEPs) were recorded from the biceps and triceps brachii at two positions, mid-elbow flexion and extension, while cycling at 5% and 15% of peak power output. While phase-dependent modulation of MEP and CMEP amplitudes occurred in the biceps brachii, there was no difference between flexion and extension for MEP amplitudes in the triceps brachii and CMEP amplitudes were higher during flexion than extension. Furthermore, MEP amplitudes in both biceps and triceps brachii increased with increased workload. CMEP amplitudes increased with higher workloads in the triceps brachii, but not biceps brachii, though the pattern of change in CMEPs was similar to MEPs. Differences between changes in CSE between the biceps and triceps brachii suggest that these antagonistic muscles may be under different neural control during arm cycling. Putative mechanisms are discussed.