Contraction-induced upper extremity H reflexes: normative values.

Abstract

To determine the reliability of contraction-induced upper extremity H reflexes; to calculate normal values for latency, amplitude, and side-to-side variation; and to correlate latency to arm length. Case series. Electrophysiology laboratory of a tertiary care center. Twenty-three healthy volunteers (4 men, 19 women), aged 19 to 42. Volunteers were tested bilaterally for H reflexes in four to six upper extremity muscles during an isometric contraction. H reflex onset latency, onset to negative peak amplitude, side-to-side variation, normal ranges, and latency versus arm-length correlation. H reflexes were found at all 264 sites tested. Mean latencies varied from 9.5 to 27 msec. Maximum normal side-to-side variation was 1.5 to 2.7 msec. Maximum normal amplitude ratios (larger to smaller) ranged from 2.06 to 4.80. Abductor pollicis brevis (APB) and abductor digiti minimi (ADM) H reflex latencies were strongly correlated to arm length. Correlation for APB = .64 (p<.0001) and for ADM = .70 (p<.0001). Contraction-induced upper extremity H reflexes occur consistently in healthy adults, with latencies, amplitudes, and side-to-side variation occurring in predictable ranges.