Abstract
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.
Highlights
The basic pattern of rhythmic and alternating locomotor outputs in humans, such as arm cycling, are partially mediated via a spinally located network of neurones referred to as a central pattern generator (CPG) [1,2,3,4,5], though supraspinal input is required [6,7,8]
We recently showed that corticospinal excitability (CSE) to the biceps brachii was higher during the elbow flexion phase of arm cycling compared to an intensity-matched tonic contraction
cervicomedullary evoked potentials (CMEPs) expressed as a percentage of Mmax were 18%, and 1.16% during the 5% peak power output (PPO) trial and 31.5% and
Summary
The basic pattern of rhythmic and alternating locomotor outputs in humans, such as arm cycling, are partially mediated via a spinally located network of neurones referred to as a central pattern generator (CPG) [1,2,3,4,5], though supraspinal input is required [6,7,8]. Studies have typically assessed spinal reflex modulation during locomotor outputs as a means to understand the neural control mechanisms underlying their production [9,10]. The results from these studies show that spinal reflexes, and the processing of sensory information, are both muscle- and phase- Zehr and Chua (2000) [11] demonstrated that cutaneous reflexes in some arm muscles were related to the amplitude of the ongoing background EMG (i.e., contraction intensity) while other muscles (e.g., biceps brachii) showed phase-dependent modulation.
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