Received September 1, 2005
Revised September 15, 2005
Accepted after revision October 4, 2005
Human/environmental and exercise physiology
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MAXIMAL MOTOR UNIT FIRING RATES DURING ISOMETRIC RESISTANCE TRAINING
Angela Pucci 1,
Lisa Griffin 2*,
E. Cafarelli 1
1 York University
2 University of Texas at Austin
* To whom correspondence should be addressed. E-mail: l.griffin{at}mail.utexas.edu.
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Abstract |
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This study measured changes in maximal voluntary contraction (MVC) force, percent maximal activation, maximal surface EMG, M-wave amplitude and average motor unit firing rates during the initial three weeks of isometric resistance training of the quadriceps muscle. Ten individuals participated in a resistance training program three times a week for three weeks and ten participated as a control group. In the training group, MVC increased by 35% (from 761 ± 77 N to 1031 ± 78 N) by the end of the 3 weeks. There were no changes in mean motor unit firing rates during submaximal or maximal voluntary contractions of 50 (15.51 ± 1.48 Hz), 75 (20.23 ± 1.85 Hz) or 100 (42.25 ± 2.72 Hz) % MVC with isometric resistance training. There was also no change in maximal surface EMG relative to the M wave amplitude. However, there was a small increase in maximal activation (95.7 ± 1.83 % to 98.44 ± 0.66 %) as measured by the twitch interpolation technique. There were no changes in any of the parameters measured in the control group. It is suggested that mechanisms other than increases in average motor unit firing rates contributed to the increase in maximal force output with resistance training. Such mechanisms may include a combination of increased motor unit recruitment, enhanced protein synthesis, and changes in motor unit synchronization and muscle activation patterns across the quadriceps synergy.
Key Words:
EMG, Motor control
