Relationships between voluntary activation and motor unit firing rate during maximal voluntary contractions in young and older adults

The extent to which an individual can voluntarily produce maximal muscular force can be estimated using the interpolated twitch technique. Incompleteness of activation is typically attributed to either incomplete recruitment, suboptimal firing rates or both of these mechanisms. The purpose of this s...

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Bibliographic Details
Published in:European journal of applied physiology 2008-08, Vol.103 (6), p.625-630
Main Authors: Knight, Christopher A., Kamen, Gary
Format: Article
Language:English
Subjects:
Adult
Age Factors
Aged
Aged, 80 and over
Biomedical and Life Sciences
Biomedicine
Electric Stimulation
Exercise - physiology
Female
Human Physiology
Humans
Knee
Male
Motor Neurons - physiology
Muscle Contraction
Muscle Strength
Muscle, Skeletal - innervation
Occupational Medicine/Industrial Medicine
Original Article
Recruitment, Neurophysiological
Sports Medicine
Torque
Volition
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Summary:The extent to which an individual can voluntarily produce maximal muscular force can be estimated using the interpolated twitch technique. Incompleteness of activation is typically attributed to either incomplete recruitment, suboptimal firing rates or both of these mechanisms. The purpose of this study was to assess the relationship between muscle activation and maximal motor unit firing rates. Measures of muscle activation and motor unit firing rates during maximal effort contractions were obtained from 15 subjects (8 young, 7 older) throughout a 6-week strength training program for the knee extensors. High resolution interpolated twitch responses were obtained using a circuit that removes the force level of the maximal voluntary contraction prior to amplification of the additional evoked force. Maximal firing rates were obtained using a four-wire needle electrode. Electrical stimulation of the knee extensors during maximal effort contractions evoked a transient increase in the force and the amplitude of this additional force was correlated with maximal firing rates at r  = −0.62 ( p  
ISSN:1439-6319
1439-6327
DOI:10.1007/s00421-008-0757-z