Introduction: This study examines effects of low-threshold afferents from the brachioradialis (BR) on excitability of triceps brachii (TB) motor neurons in humans.
Methods: We evaluated the effects using a post stimulus time histogram (PSTH) and electromyogram averaging (EMG-A) methods in 13 healthy human participants. Electrical conditioning stimulation to the radial nerve branch innervating BR with the intensity below the motor threshold was delivered.
Results: In the PSTH study, the stimulation produced a trough (inhibition) in 36/69 TB motor units for all the participants. A cutaneous stimulation never provoked such inhibition. The central latency of the inhibition was 1.5 ± 0.5 ms longer than that of the homonymous facilitation. In the EMG-A study, the stimulation produced inhibition in EMG-A of TB in all participants. The inhibition diminished with a tonic vibration stimulation to BR.
Discussion: These findings suggest that oligosynaptic inhibition mediated by group Ia afferents from BR to TB exists in humans. Muscle Nerve 57: 122-128, 2018.
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