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This Article Full Text Full Text (PDF) All Versions of this Article: 94/1/387    most recent 01182.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Gazzoni, M. Articles by Farina, D. Search for Related Content PubMed PubMed Citation Articles by Gazzoni, M. Articles by Farina, D.

Conduction Velocity of Quiescent Muscle Fibers Decreases During Sustained Contraction

¹Laboratorio di Ingegneria del Sistema Neuromusculore, Dipartimento di Elettronica, Politecnico di Torino, Torino, Italy; and ²Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark

Submitted 16 November 2004; accepted in final form 6 February 2005

We tested the hypothesis that conduction velocity of quiescent muscle fibers decreases during sustained contraction due to the activity of the active motor units in the muscle. Ten subjects trained for the identification of a target motor unit in the abductor pollicis brevis with feedback on surface EMG signals detected with a two-dimensional array of 61 electrodes. The subjects activated the target motor unit in two 10-s long contractions, before (contraction C1) and after (C3) a 3-min contraction (C2), all in ischemic condition. The target motor unit was not activated during C2. Eight of the 10 subjects (control group) performed a second experimental session identical to the first but with a resting period of 3 min instead of the contraction C2. Exerted force and target motor unit discharge rate were not different between the two subject groups and between C1 and C3 (mean ± SD, over C1 and C3; C2 group: 15.8 ± 10.4% maximal voluntary contractions and 13.1 ± 1.9 pps; control group: 15.6 ± 22.1% maximal voluntary contractions and 14.5 ± 1.9 pps, respectively). Muscle fiber conduction velocity of the target motor unit decreased in C3 with respect to C1 in the C2 group (3.59 ± 0.57 and 3.34 ± 0.47 m/s for C1 and C3, respectively; P < 0.05) but not in the control group (3.47 ± 0.68 and 3.46 ± 0.73 m/s). In the C2 group, the percent decrease in conduction velocity of the target motor unit between C1 and C3 (6.4 ± 7.1%) was not significantly different from the percent decrease in the average conduction velocity of the motor units active during C2 (9.6 ± 5.4%). In conclusion, the contraction-induced modifications in electrophysiological membrane properties of muscle fibers are partly independent on fiber activation.