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

Arm-cycling is a versatile exercise modality with applications in both athletic enhancement and rehabilitation, yet the influence of forearm orientation remains understudied. Thus, this study aimed to investigate the impact of forearm position on upper-body arm-cycling Wingate tests. Fourteen adult males (27.3 ± 5.8 years) underwent bilateral assessments of handgrip strength in standing and seated positions, followed by pronated and supinated forward arm-cycling Wingate tests. Electromyography (EMG) was recorded from five upper-extremity muscles, including anterior deltoid, triceps brachii lateral head, biceps brachii, latissimus dorsi, and brachioradialis. Simultaneously, bilateral normal and propulsion forces were measured at the pedal-crank interface. Rate of perceived exertion (RPE), power output, and fatigue index were recorded post-test. The results showed that a pronated forearm position provided significantly (p < 0.05) higher normal and propulsion forces and triceps brachii muscle activation patterns during arm-cycling. No significant difference in RPE was observed between forearm positions (p = 0.17). A positive correlation was found between seated handgrip strength and peak power output during the Wingate test while pronated (dominant: p = 0.01, r = 0.55; non-dominant: p = 0.03, r = 0.49) and supinated (dominant: p = 0.03, r = 0.51; don-dominant: p = 0.04, r = 0.47). Fatigue changed the force and EMG profile during the Wingate test. In conclusion, this study enhances our understanding of forearm position's impact on upper-body Wingate tests. These findings have implications for optimizing training and performance strategies in individuals using arm-cycling for athletic enhancement and rehabilitation.

Interhemispheric inhibition is different during arm cycling than a position- and intensity-matched tonic contraction.

Task-dependent changes in inhibition may explain why supraspinal excitability is higher during arm cycling than an intensity- and position-matched tonic contraction. The present study investigated whether interhemispheric inhibition (IHI) associated with biceps brachii activity was different during arm cycling, a locomotor output, compared to a tonic contraction. IHI was quantified using an ipsilateral silent period (iSP) evoked via transcranial magnetic stimulation (TMS) of the ipsilateral motor cortex. TMS was delivered at 120% resting motor threshold during the mid-elbow flexion phase of arm cycling (6 o'clock position, made relative to a clock face) and during a position- and intensity-matched tonic contraction. In total, 36 participants took part in the study. However, only 14 participants demonstrated IHI during arm cycling and 10 participants during tonic contraction. Of these participants, eight displayed clear iSPs during arm cycling and tonic contraction. The iSP duration was longer during arm cycling than tonic contraction (p < 0.05), while iSP EMG amplitude and area were not different between tasks (p > 05 for both comparisons). The main finding from this study is that IHI appears to be stronger during arm cycling than an intensity- and position-matched tonic contraction. This does not support previous findings of higher supraspinal excitability during arm cycling.

Endurance-exercise training adaptations in spinal motoneurones: potential functional relevance to locomotor output and assessment in humans.

It is clear from non-human animal work that spinal motoneurones undergo endurance training (chronic) and locomotor (acute) related changes in their electrical properties and thus their ability to fire action potentials in response to synaptic input. The functional implications of these changes, however, are speculative. In humans, data suggests that similar chronic and acute changes in motoneurone excitability may occur, though the work is limited due to technical constraints. To examine the potential influence of chronic changes in human motoneurone excitability on the acute changes that occur during locomotor output, we must develop more sophisticated recording techniques or adapt our current methods. In this review, we briefly discuss chronic and acute changes in motoneurone excitability arising from non-human and human work. We then discuss the potential interaction effects of chronic and acute changes in motoneurone excitability and the potential impact on locomotor output. Finally, we discuss the use of high-density surface electromyogram recordings to examine human motor unit firing patterns and thus, indirectly, motoneurone excitability. The assessment of single motor units from high-density recording is mainly limited to tonic motor outputs and minimally dynamic motor output such as postural sway. Adapting this technology for use during locomotor outputs would allow us to gain a better understanding of the potential functional implications of endurance training-induced changes in human motoneurone excitability on motor output.

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

The use of transcranial magnetic stimulation to assess the excitability of the central nervous system to further understand the neural control of human movement is expansive. The majority of the work performed to-date has assessed corticospinal excitability either at rest or during relatively simple isometric contractions. The results from this work are not easily extrapolated to rhythmic, dynamic motor outputs, given that corticospinal excitability is task-, phase-, intensity-, direction-, and muscle-dependent (Power KE, Lockyer EJ, Forman DA, Button DC. Appl Physiol Nutr Metab 43: 1176-1185, 2018). Assessing corticospinal excitability during rhythmic motor output, however, involves technical challenges that are to be overcome, or at the minimum considered, when attempting to design experiments and interpret the physiological relevance of the results. The purpose of this narrative review is to highlight the research examining corticospinal excitability during a rhythmic motor output and, importantly, to provide recommendations regarding the many factors that must be considered when designing and interpreting findings from studies that involve limb movement. To do so, the majority of work described herein refers to work performed using arm cycling (arm pedaling or arm cranking) as a model of a rhythmic motor output used to examine the neural control of human locomotion.

Short-interval intracortical inhibition of the biceps brachii in chronic-resistance versus non-resistance-trained individuals.

The purpose of this study was to investigate the effects of chronic resistance training on corticospinal excitability and short intracortical inhibition of the biceps brachii. Eight chronic resistance-trained (RT) and eight non-RT participants completed one experimental session including a total of 30 brief (7 s) elbow flexors isometric contractions at various force outputs [15, 25 and 40% of maximum voluntary contraction (MVC)]. Before the contractions, MVC, maximal compound muscle action potential (Mmax) during 5% MVC and active motor threshold (AMT) at the three various force outputs were recorded. MVC force of the chronic-RT group was 24% higher than the non-RT group (p ≤ 0.001; ω2 = 0.72). The chronic-RT group had lower AMTs at targeted forces of 15 and 25% MVC (p = 0.022 and p = 0.012, respectively) compared to the non-RT group. During 25 and 40% of MVC, the non-RT group exhibited decreased SICI in comparison to the chronic-RT group (p = 0.008; ω2 = 0.35 and p = 0.03; ω2 = 0.21, respectively). However, SICI did not differ between groups at 15% MVC (p = 0.62). In conclusion, chronic resistance training significantly reduces SICI. This suggests the presence of an adaptive process of inhibitory and facilitatory network activation, which may cancel out the SICI, allowing for increased corticomotor drive to the exercised muscle following a long period of resistance training.

Sex-related differences in corticospinal excitability outcome measures of the biceps brachii during a submaximal elbow flexor contraction.

The purpose of this study was to investigate the effects of sex, muscle thickness, and subcutaneous fat thickness (SFT) on corticospinal excitability outcome measures of the biceps brachii. Eighteen participants (10 males and 8 females) completed this study. Ultrasound was used to assess biceps brachii muscle thickness and the overlying SFT. Transcranial magnetic stimulation (TMS) was used to determine corticospinal excitability by inducing motor-evoked potentials (MEPs) at eight different TMS intensities from 90% to 160% of active motor threshold (AMT) from the biceps brachii during an isometric contraction of the elbow flexors at 10% of maximum voluntary contraction (MVC). Biceps brachii maximal compound muscle action potential (Mmax) was also recorded prior to and after TMS. Males had higher (p < 0.001) biceps brachii muscle thickness and lower SFT, produced higher levels of MVC force and had, on average, higher (p < 0.001) MEP amplitudes at lower (p < 0.05) percentages of maximal stimulator output than females during the 10% elbow flexion MVC. Multiple linear regression modeling revealed that sex was not associated with any of the neurophysiological parameters examined, while SFT showed a positive association with the stimulation intensity required at AMT (p = 0.035) and a negative association with biceps brachii pre-stimulus electromyography (EMG) activity (p = 0.021). Additionally, there was a small positive association between muscle thickness and biceps brachii pre-stimulus EMG activity (p = 0.049). Overall, this study suggests that some measures of corticospinal excitability may be different between the sexes and influenced by SFT and muscle thickness.

Two weeks of arm cycling sprint interval training enhances spinal excitability to the biceps brachii.

The present study aimed to investigate whether a 2-wk arm cycling sprint interval training (SIT) program modulated corticospinal pathway excitability in healthy, neurologically intact participants. We employed a pre-post study design with two groups: 1) an experimental SIT group and 2) a nonexercising control group. Transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of corticospinal axons were used at baseline and post-training to provide indices of corticospinal and spinal excitability, respectively. Stimulus-response curves (SRCs) recorded from the biceps brachii were elicited for each stimulation type during two submaximal arm cycling conditions [25 watts (W) and 30% peak power output (PPO)]. All stimulations were delivered during the mid-elbow flexion phase of cycling. Compared with baseline, performance on the time-to-exhaustion (TTE) test at post-testing was improved for members of the SIT group but was not altered for controls, suggesting that SIT improved exercise performance. There were no changes in the area under the curve (AUC) for TMS-elicited SRCs for either group. However, the AUC for TMES-elicited cervicomedullary motor-evoked potential SRCs were significantly larger at post-testing in the SIT group only (25 W: P = 0.012, d = 0.870; 30% PPO: P = 0.016, d = 0.825). This data shows that overall corticospinal excitability is unchanged following SIT, whereas spinal excitability is enhanced. Although the precise mechanisms underlying these findings during arm cycling at post-SIT are unknown, it is suggested that the enhanced spinal excitability may represent a neural adaptation to training.NEW & NOTEWORTHY Two weeks of arm cycling sprint interval training (SIT) improves subsequent aerobic exercise performance and induces changes within the descending corticospinal pathway. Specifically, spinal excitability is enhanced following training, whereas overall corticospinal excitability does not change. These results suggest that the enhanced spinal excitability may represent a neural adaptation to training. Future work is required to discern the precise neurophysiological mechanisms underlying these observations.

Interhemispheric inhibition to the biceps brachii during arm cycling.

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.

Neuromuscular fatigue of the elbow flexors during repeated maximal arm cycling sprints: the effects of forearm position.

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.

Modulation of Corticospinal Excitability with Contralateral Arm Cycling.

This is the first study to examine the influence of activity in one limb on corticospinal excitability to the contralateral limb during a locomotor output. Corticospinal and spinal excitability to the biceps brachii of the ipsilateral arm were assessed using transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of corticospinal axons, respectively. Responses were evoked during the mid-elbow extension position of arm cycling across three different cycling tasks: (1) bilateral arm cycling (BL), (2) unilateral, contralateral cycling with the ipsilateral arm moving passively (IP), and (3) unilateral, contralateral cycling with the ipsilateral arm at rest (IR). Each of these three tasks were performed at two cadences: 60 and 90 rpm. TMS-induced motor evoked potential (MEPs) amplitudes were significantly smaller during BL compared to the IP and IR conditions; however, MEP amplitudes were not significantly different between IP and IR. TMES-evoked cervicomedullary MEP (CMEPs) amplitudes followed a similar pattern of task-dependent modulation, with BL having the smallest CMEPs and IR having the largest. In line with our previous findings, MEP amplitudes increased and CMEP amplitudes decreased as the cadence increased from 60 to 90 rpm. We suggest that the higher corticospinal excitability to the ipsilateral limb during the IP and IR conditions was predominantly due to disinhibition at both the cortical and spinal levels.

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

The purpose of this study was to evaluate corticospinal excitability to the biceps and triceps brachii during forward (FWD) and backward (BWD) arm cycling. Corticospinal and spinal excitability were assessed using transcranial magnetic stimulation and transmastoid electrical stimulation to elicit motor evoked potentials (MEPs) and cervicomedullary evoked potentials (CMEPs), respectively. MEPs and CMEPs were recorded from the biceps and triceps brachii during FWD and BWD arm cycling at 2 positions, 6 and 12 o'clock. The 6 o'clock position corresponded to mid-elbow flexion and extension during FWD and BWD cycling, respectively, while 12 o'clock corresponded to mid-elbow extension and flexion during FWD and BWD cycling, respectively. During the flexion phase, MEP and CMEP amplitudes of the biceps brachii were higher during FWD cycling. However, during the extension phase, MEP and CMEP amplitudes were higher during BWD cycling. For the triceps brachii, MEP amplitudes were higher during FWD cycling regardless of phase. However, CMEP amplitudes were phase-dependent. During the flexion phase, CMEPs of the triceps brachii were higher during FWD cycling compared with BWD, but during the extension phase CMEPs were higher during BWD cycling compared with FWD. The data suggest that corticospinal and spinal excitability to the biceps brachii is phase- and direction-dependent. In the triceps brachii, spinal, but not corticospinal, excitability is phase-dependent when comparing FWD and BWD cycling. Novelty This is the first study to assess corticospinal excitability during FWD and BWD locomotor output. Corticospinal excitability during arm cycling depends on the direction, phase, and muscle being assessed.

Corticospinal-Evoked Responses from the Biceps Brachii during Arm Cycling across Multiple Power Outputs.

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.

Corticospinal Excitability to the Biceps Brachii is Not Different When Arm Cycling at a Self-Selected or Fixed Cadence.

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.

Delayed-Onset Muscle Soreness and Topical Analgesic Alter Corticospinal Excitability of the Biceps Brachii.

INTRODUCTION: The interactive effect of delayed-onset muscle soreness (DOMS) and a topical analgesic on corticospinal excitability was investigated. METHODS: Thirty-two participants completed Experiments A (no DOMS) and B (DOMS). For each experiment, participants were randomly assigned to two groups: 1) topical analgesic gel (topical analgesic, n = 8), or 2) placebo gel (placebo, n = 8) group. Before the application of gel (pregel), as well as 5, 15, 30, and 45 min postgel, motor-evoked potential (MEP) area, latency, and silent period, as well as cervicomedullary MEP and maximal compound motor unit action potential areas and latencies were measured. In addition, pressure-pain threshold (PPT) was measured pre-DOMS and at the same timepoints in experiment B. RESULTS: In experiment A, neither group showed a significant change for any outcome measure. In experiment B, both groups exhibited a significant decrease in PPT from pre-DOMS to pregel. After the application of topical analgesic, but not placebo, there was a significant increase in PPT at 45 min postgel, respectively, compared with pregel and a main effect of time for the silent period to increase compared with pregel. Participants with DOMS had reduced MEP and cervicomedullary MEP areas and increased corticospinal silent periods compared with those who did not have DOMS. CONCLUSIONS: These findings suggest that DOMS reduced corticospinal excitability and after the administration of menthol-based topical analgesic, there was a reduction in pain, which was accompanied by increased corticospinal inhibition.

Modulation of motoneurone excitability during rhythmic motor outputs.

In quadrupeds, special circuity located within the spinal cord, referred to as central pattern generators (CPGs), is capable of producing complex patterns of activity such as locomotion in the absence of descending input. During these motor outputs, the electrical properties of spinal motoneurones are modulated such that the motoneurone is more easily activated. Indirect evidence suggests that like quadrupeds, humans also have spinally located CPGs capable of producing locomotor outputs, albeit descending input is considered to be of greater importance. Whether motoneurone properties are reconfigured in a similar manner to those of quadrupeds is unclear. The purpose of this review is to summarize our current state of knowledge regarding the modulation of motoneurone excitability during CPG-mediated motor outputs using animal models. This will be followed by more recent work initially aimed at understanding changes in motoneurone excitability during CPG-mediated motor outputs in humans, which quickly expanded to also include supraspinal excitability.

Bipedal hopping timed to a metronome to detect impairments in anticipatory motor control in people with mild multiple sclerosis.

BACKGROUND: People with mild multiple sclerosis (MS) often report subtle deficits in balance and cognition but display no measurable impairment on clinical assessments. We examined whether hopping to a metronome beat had the potential to detect anticipatory motor control deficits among people with mild MS (Expanded Disability Status Scale ≤ 3.5). METHODS: Participants with MS (n = 13), matched controls (n = 9), and elderly subjects (n = 13) completed tests of cognition (Montreal Cognitive Assessment (MoCA)) and motor performance (Timed 25 Foot Walk Test (T25FWT)). Participants performed two bipedal hopping tasks: at 40 beats/min (bpm) and 60-bpm in random order. Hop characteristics (length, symmetry, variability) and delay from the metronome beat were extracted from an instrumented walkway and compared between groups. RESULTS: The MS group became more delayed from the metronome beat over time whereas elderly subjects tended to hop closer to the beat (F = 4.52, p = 0.02). Delay of the first hop during 60-bpm predicted cognition in people with MS (R = 0.55, ß = 4.64 (SD 4.63), F = 4.85, p = 0.05) but not among control (R = 0.07, p = 0.86) or elderly subjects (R = 0.17, p = 0.57). In terms of hopping characteristics, at 60-bpm, people with MS and matched controls were significantly different from the elderly group. However, at 40-bpm, the MS group was no longer significantly different from the elderly group, even though matched controls and elderly still differed significantly. CONCLUSIONS: This new timed hopping test may be able to detect both physical ability, and feed-forward anticipatory control impairments in people with mild MS. Hopping at a frequency of 40-bpm seemed more challenging. Several aspects of anticipatory motor control can be measured: including reaction time to the first metronome cue and the ability to adapt and anticipate the beat over time.

Bipedal Hopping Reveals Evidence of Advanced Neuromuscular Aging Among People With Mild Multiple Sclerosis.

Measures of walking such as the timed 25-ft walk test (T25FWT) may not be able to detect subtle impairment in lower limb function among people with multiple sclerosis (MS). We examined bipedal hopping to determine to what extent people with mild (Expanded Disease Severity Scale ≤ 3.5) MS (n = 13) would differ compared to age-, gender-, and education-matched controls (n = 9) and elderly participants (n = 13; ≥ 70 years old). We estimated lower limb power (e.g., hop length, velocity), consistency (e.g., variability of hop length, time), and symmetry (ratio of left to right foot). Participants completed the T25FWT and, after a rest, they then hopped using both feet 4 times along the walkway. We found that although all groups scored below the 6 -s cutoff for T25FWT, the elderly group had significantly shorter hop lengths, more variability, and more asymmetry than the controls. The results of the MS group were not significantly different from the elderly or controls in most measures and most of their values fell between the control and elderly groups. Hop length, but not measures of walking predicted Expanded Disease Severity Scale score (R2 = .38, p = .02). Bipedal hopping is a potentially useful measure of lower limb neuromuscular performance.

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

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.