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Stimulus pulse‐width influences H‐reflex recruitment but not H max /M max ratio
Author(s) -
Lagerquist Olle,
Collins David F.
Publication year - 2008
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.20957
Subject(s) - stimulus (psychology) , reflex , h reflex , pulse (music) , physics , medicine , psychology , anesthesia , optics , detector , psychotherapist
It has been proposed that pulse‐widths of 0.5–1.0 ms should be used to evoke H‐reflexes in humans; however, the influence of pulse‐width on H‐reflex recruitment over a range of stimulus intensities has not been well characterized. We constructed soleus H‐reflex vs. M‐wave recruitment curves using 50, 200, 500, and 1000 μs pulses in 12 subjects. In contrast to previous findings, changing the pulse‐width did not significantly alter maximal H‐reflex (H max ) or M‐wave (M max ) amplitudes or H max /M max ratios. In fact, the 1000 μs pulses resulted in larger H‐reflexes when the M‐wave was 5% M max ; smaller M‐waves at H max ; and lower H‐reflex thresholds compared with 50 μs pulses. These differences reflect a leftward shift in the H‐reflex vs. M‐wave recruitment curve when using wide vs. narrow pulses and, combined with no change in the H max /M max ratios, suggest that factors other than antidromic collision in motor axons limit H max . These results support the idea that 1000 μs pulses should be used to evoke H‐reflexes and suggest that wider pulses may be beneficial to generate contractions with a greater reflex contribution when using neuromuscular stimulation for rehabilitation. Muscle Nerve, 2007