Relation between the size of motor units and the spectral characteristics of their action potentials. kazuseki@iname.com.
OBJECTIVE
The purpose of this study was to clarify the influence of the size of an individual motor unit on the spectral characteristics of its motor unit action potentials (MUAPs).


METHODS
In 4 human subjects, we first averaged the isometric force and the surface EMG signals triggered by the intramuscularly recorded action potentials of each motor unit during voluntary isometric contraction. Then, we obtained averaged twitch contraction curves, averaged MUAPs derived from surface EMG signals (S-MUAPs), and the power spectrum of the S-MUAPs. Finally, we tested for correlations among these results in each subject.


RESULTS
There was a positive correlation among the mean power frequency of the S-MUAPs, the maximal amplitude of the S-MUAPs, and the maximal twitch tension of their motor unit in each subject (r = 0.58-0.85; P < 0.05).


CONCLUSIONS
Since the twitch tension and the amplitude of the S-MUAPs are well-known predictors of the size of motor units, we conclude that the spectral characteristics of the S-MUAPs reflect the size of the motor unit from which they originate.
Seki
K
K
Department of Exercise Physiology, International Budo University, Katsuura, Chiba, Japan.
Narusawa
M
M
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D004576:Electromyography; D006225:Hand; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D009929:Organ Size