RESUMO
BACKGROUND: Although H reflexes cannot be reliably recorded from resting human hand intrinsic muscles, a short latency R1 response, thought to be similar to the H reflex, is readily obtained from upper extremity muscles during voluntary contraction. METHODS: The right and left median nerves of 20 normal subjects were repetitively stimulated at 3 Hz at stimulus intensities corresponding to threshold and 20%, 40% and 60% of maximal M response, recording from the abductor pollicis brevis muscle. Studies were done during both minimal and moderate voluntary contraction. RESULTS: The R1 response was present in all subjects at the 40% stimulation intensity level during moderate contraction. The mean latency was 27 ms (SD 1.77 ms) with a good correlation to arm length. The mean amplitude was 1.17 mV (SD 0.79 mV). CONCLUSIONS: Abductor pollicis muscle R1 response can be reliably measured, although latency showed much less intersubject and side to side variability than amplitude. This technique may be useful for the assessment of demyelinative lesions of the inferior segments of the brachial plexus and C8-T1 roots.