Relationship between innervation zone width and mean muscle fiber conduction velocity during a sustained isometric contraction.
OBJECTIVE
To examine the relationship between the biceps brachii muscle innervation zone (IZ) width and the mean muscle fiber conduction velocity (MFCV) during a sustained isometric contraction.


METHODS
Fifteen healthy men performed a sustained isometric elbow flexion exercise at their 60% maximal voluntary contraction (MVC) until they could not maintain the target force. Mean MFCV was estimated through multichannel surface electromyographic recordings from a linear electrode array. Before exercise, IZ width was quantified. Separate non-parametric one-way analyses of variance (ANOVAs) were used to examine whether there was a difference in each mean MFCV variable among groups with different IZ width. In addition, separate bivariate correlations were also performed to examine the relationships between the IZ width and the mean MFCV variables during the fatiguing exercise.


RESULTS
There was a significant difference in the percent decline of mean MFCV (%ΔMFCV) among groups with different IZ width (χ(2) (3)=11.571, p=0.009). In addition, there was also a significant positive relationship between the IZ width and the %ΔMFCV (Kendall's tau= 0.807; p<0.001).


CONCLUSIONS
We believe that such relationship is likely influenced by both muscle fiber size and the muscle fiber type composition.
Biophysics Laboratory, Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma 73019, USA.
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D000200:Action Potentials / Q000502:physiology; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D055815:Young Adult