Submaximal motor unit firing rates after 8 wk of isometric resistance training.
OBJECTIVE
The purpose of this study was to test the hypothesis that average motor unit firing rates change in parallel with the contractile properties of vastus lateralis following 8 wk of isometric resistance training.


METHODS
The firing rates from more than 400 motor units of vastus lateralis were obtained during voluntary isometric contractions of 50% MVC, before and again after training in male subjects (N = 10) and their untrained controls (N = 10). Single motor unit spike trains were recorded with tungsten microelectrodes.


RESULTS
Training resulted in a 36% (P < 0.05) increase in MVC. We also found significant increases (P < 0.05) in maximal twitch amplitude (+17%), time to peak tension (+9%) and the maximal instantaneous rate of contraction (+20%) in the trained leg of the experimental group. Neither the maximal integrated EMG nor the rate of increase of integrated EMG was different after training. There were no significant changes in any of these measures from the untrained leg or the control group. Average firing rates were not different after training despite the increase in twitch contractile speed.


CONCLUSIONS
These findings suggest that the control properties of the nervous system are not altered despite sizable changes in the contractile properties of muscle following 8 wk of resistance training.
Rich
C
C
Kinesiology and Health Science, Faculty of Pure and Applied Science, York University, Toronto, Ontario, Canada.
Cafarelli
E
E
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D004576:Electromyography / Q000295:instrumentation; D005267:Femoral Nerve / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007866:Leg; D008297:Male; D008839:Microelectrodes; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D014414:Tungsten; D014891:Weight Lifting / Q000502:physiology*
D014414:Tungsten