Inference of motor unit recruitment order in voluntary and electrically elicited contractions.

The relationship between surface myoelectric signal parameters and the level of voluntary or electrically elicited contractions was studied in 32 experiments on the tibialis anterior muscle of 22 healthy human subjects. Contractions were performed at 20 and 80% of the maximum voluntary contraction torque. Two levels of stimulation current were used, yielding, respectively, a maximum M wave and an M wave approximately 30% of the maximum. A four-bar electrode probe was used to detect single- and double-differential signals from which mean and median frequency of the power spectrum and average muscle fiber conduction velocity were estimated. Measurements obtained from voluntary contractions showed a positive correlation between contraction levels and both conduction velocity and spectral parameters. Conduction velocity increased by 21.2 +/- 10.9% when voluntary contraction level increased from 20 to 80% of the maximal value. Spectral parameters increased by similar amounts. Tetanic electrical stimulation was applied to a muscle motor point for 20 s via surface electrodes. Rectangular current pulses with 0.1-ms width and frequencies of 20, 25, 30, 35, and 40 Hz were used. Four types of behavior were observed with increasing stimulation level: 1) the two spectral parameters and conduction velocity both increased with stimulation in 15 experiments, 2) the two spectral parameters decreased and conduction velocity increased in 8 experiments, 3) the two spectral parameters and conduction velocity both decreased in 6 experiments, and 4) the two spectral parameters increased and conduction velocity decreased in 3 experiments. Conduction velocity increased with increasing stimulation current in 72% of the experiments, indicating a recruitment order similar to that of voluntary contractions, although it decreased in the other 28% of the cases, indicating a reverse order of recruitment. Contrary to what is observed in direct stimulation of nerves, motor units are not in general recruited in reverse order of size during electrical stimulation of a muscle motor point. This discrepancy may be the result of geometric factors or a lack of correlation between axonal branch diameter and the diameter of the parent motoneuron axon. Changes of conduction velocity and spectral parameters in opposite directions may be the result of the combined effect of the motor unit recruitment order and of the different tissue filtering function associated with the geometric location of the recruited motor units within the muscle.

[1]  F BUCHTHAL,et al.  Propagation velocity in electrically activated muscle fibres in man. , 1955, Acta physiologica Scandinavica.

[2]  C. Håkansson.  Conduction velocity and amplitude of the action potential as related to circumference in the isolated fibre of frog muscle. , 1956, Acta physiologica Scandinavica.

[3]  S. Siegel,et al.  Nonparametric Statistics for the Behavioral Sciences. , 1957 .

[4]  H. J. Seddon,et al.  New Developments in Electromyography and Clinical Neurophysiology , 1974 .

[5]  P. Lawrence,et al.  Electrocutaneous Nerve Stimulation-II: Stimulus Waveform Selection , 1979, IEEE Transactions on Biomedical Engineering.

[6]  F Buchthal,et al.  Motor unit of mammalian muscle. , 1980, Physiological reviews.

[7]  J. Rinzel,et al.  The dependence of impulse propagation speed on firing frequency, dispersion, for the Hodgkin-Huxley model. , 1981, Biophysical journal.

[8]  B. Bigland-ritchie,et al.  Conduction velocity and EMG power spectrum changes in fatigue of sustained maximal efforts. , 1981, Journal of applied physiology: respiratory, environmental and exercise physiology.

[9]  J. Daube,et al.  Muscles Alive , 1981, Neurology.

[10]  D. M. Lewis,et al.  The Physiology of Motor Units in Mammalian Skeletal Muscle , 1981 .

[11]  Tadashi Masuda,et al.  The Measurement of Muscle Fiber Conduction Velocity Using a Gradient Threshold Zero-Crossing Method , 1982, IEEE Transactions on Biomedical Engineering.

[12]  Alan J. McComas,et al.  Impulse conduction velocities in human biceps brachii muscles , 1983, Experimental Neurology.

[13]  J. Mortimer,et al.  The Effect of Stimulus Parameters on the Recruitment Characteristics of Direct Nerve Stimulation , 1983, IEEE Transactions on Biomedical Engineering.

[14]  Kevin C. McGill,et al.  High-Resolution Alignment of Sampled Waveforms , 1984, IEEE Transactions on Biomedical Engineering.

[15]  C. J. Luca.  Myoelectrical manifestations of localized muscular fatigue in humans. , 1984 .

[16]  T. Moritani,et al.  Electromechanical changes during electrically induced and maximal voluntary contractions: Electrophysiologic responses of different muscle fiber types during stimulated contractions , 1985, Experimental Neurology.

[17]  L. Arendt-Nielsen,et al.  The relationship between mean power frequency of the EMG spectrum and muscle fibre conduction velocity. , 1985, Electroencephalography and clinical neurophysiology.

[18]  Carlo J. De Luca,et al.  A Note on the Noninvasive Estimation of Muscle Fiber Conduction Velocity , 1985, IEEE Transactions on Biomedical Engineering.

[19]  F E Zajac,et al.  Relationship among recruitment order, axonal conduction velocity, and muscle-unit properties of type-identified motor units in cat plantaris muscle. , 1985, Journal of neurophysiology.

[20]  C. D. De Luca,et al.  Myoelectric signal conduction velocity and spectral parameters: influence of force and time. , 1985, Journal of applied physiology.

[21]  G. Zilvold,et al.  The measurement of the conduction velocity of muscle fibres with surface EMG according to the cross-correlation method. , 1985, Electromyography and clinical neurophysiology.

[22]  C. D. De Luca,et al.  Effects of electrode location on myoelectric conduction velocity and median frequency estimates. , 1986, Journal of applied physiology.

[23]  R. D'ambrosia,et al.  The Myoelectric Signal of Electrically Stimulated Muscle During Recruitment: An Inherent Feedback Pareter for a Closed-Loop Control Scheme , 1986, IEEE Transactions on Biomedical Engineering.

[24]  T. Helliwell,et al.  THE MORPHOLOGY AND MORPHOMETRY OF THE NORMAL HUMAN TIBIALIS ANTERIOR MUSCLE , 1987, Neuropathology and applied neurobiology.

[25]  J R Westbury,et al.  Associations between spectral representation of the surface electromyogram and fiber type distribution and size in human masseter muscle. , 1987, Electromyography and clinical neurophysiology.

[26]  T. Masuda,et al.  Changes of the average muscle fiber conduction velocity during a varying force contraction. , 1987, Electroencephalography and clinical neurophysiology.

[27]  R. Merletti,et al.  Suppression of stimulation artifacts from myoelectric-evoked potential recordings , 1988, IEEE Transactions on Biomedical Engineering.