Comparison of the recruitment and discharge properties of motor units in human brachial biceps and adductor pollicis during isometric contractions

doi:10.1016/0006-8993(81)90266-3

Brain Research

Volume 219, Issue 1, 24 August 1981, Pages 45-55

https://doi.org/10.1016/0006-8993(81)90266-3 Get rights and content

Abstract

Experiments were designed to assess the relative contribution of rate coding and motor unit recruitment to force production in two muscles of different fiber composition and function. Single motor unit action potentials were recorded during steady isometric contraction in biceps brachii, a large proximal limb muscle of mixed fiber composition, and adductor pollicis, a small hand muscle comprised mainly of type I muscle fibers. Action potential spike trains were obtained over the entire force range in each muscle. The results suggest that these two muscles are controlled in different ways. In biceps brachii, recruitment was observed from 0 to 88% maximum voluntary contraction (MVC). In adductor pollicis, no motor unit was observed to be recruited at forces greater than 50% MVC, with the majority of recruitment occuring below 30% MVC. On the average, motor units in adductor pollicis discharged at higher rates, with less regularity, and with a greater frequency of occurrence of short interspike intervals (intervals ≤ 20 msec) than those in biceps brachii. Such findings suggest that rate coding plays a more prominent role in force modulation in adductor pollicis, while recruitment plays a more important role throughout the contractile force range in biceps brachii.

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Comparison of the recruitment and discharge properties of motor units in human brachial biceps and adductor pollicis during isometric contractions

Abstract

Brain Research

Biophys. J.

Physiol. Behav.

J. Neurol. Sci.

Brain Research

Exp. Neurol.

The discharge of impulses in motor nerve fibres. I. Impulses in single fibres of the phrenic nerve

J. Physiol. (Lond.)

The discharge of impulses in motor nerve fibres. II. The frequency of discharge in reflex and voluntary contraction

J. Physiol. (Lond.)

A new bipolar indwelling electrode for electromyography

J. appl. Physiol.

Motor unit activity in the voluntary contractions of human muscle

J. Physiol. (Lond.)

Anatomy of medial gastrocnemius and soleus motor nuclei in cat spinal cord

J. Neurophysiol.

Activity of single motor units during isometric tension

Neurology

Quantitative measures of output of a motoneuron pool during monosynaptic reflexes

J. Neurophysiol.

Relation between firing frequency of motor units and muscle tension in the human

Electromyography

Ballistic contractions in man: characteristic recruitment pattern of single motor units of the tibialis anterior muscle

J. Physiol. (Lond.)

Ballistic contractions in fast or slow human muscles: discharge patterns of single motor units

J. Physiol. (Lond.)