Experimental muscle pain decreases the frequency threshold of electrically elicited muscle cramps |
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Authors: | Mariano Serrao Lars Arendt-Nielsen Hong-You Ge Francesco Pierelli Giorgio Sandrini Dario Farina |
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Institution: | (1) Rehabilitation Unit, Polo Pontino-ICOT, Latina, University of Rome “La Sapienza”, Rome, Italy;(2) Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, 9220 Aalborg, Denmark;(3) Department of Neurological Sciences, IRCCS “C. Mondino” Foundation, University of Pavia, Pavia, Italy |
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Abstract: | This study in humans tested the hypothesis that nociceptive muscle afferent input facilitates the occurrence of muscle cramps.
In 13 healthy adults, muscle cramps were experimentally induced in the foot by stimulating the tibialis posterior nerve at
the ankle with 2-s bursts of stimuli separated by 30 s, with stimulation frequency increasing by 2-Hz increments from 10 Hz
until the cramp appeared. The minimum stimulation frequency that induced the cramp was defined “cramp frequency threshold”.
In 2 days, elicitation of the cramp was performed in the two-feet with and without (baseline condition) injection of hypertonic
(painful condition) or isotonic (control condition) saline into the deep midportion of the flexor hallucis brevis muscle,
from where surface EMG signals were recorded. The cramp frequency threshold was lower for the painful condition with respect
to its baseline (mean ± SE, hypertonic saline: 25.7 ± 2.1 Hz, corresponding baseline: 31.2 ± 2.8 Hz; P < 0.01) while there was no difference between the threshold with isotonic injection with respect to baseline. EMG average
rectified value and power spectral frequency were higher during the cramp than immediately before the stimulation that elicited
the cramp (pre-cramp: 13.9 ± 1.6 μV and 75.4 ± 3.8 Hz, respectively; post-cramp: 19.9 ± 3.2 μV and 101.6 ± 6.0 Hz; P < 0.05). The results suggest that nociceptive muscle afferent activity induced by injection of hypertonic saline facilitates
the generation of electrically elicited muscle cramps. |
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Keywords: | Muscle cramps Nociceptive fibers Cramp threshold Experimental muscle pain |
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