Summary
Most skeletal muscles include at least two types of MU's. Then, it has been stated that the properties of each MU may imply its specific recruitment in static or dynamic work.
To test this hypothesis, the activities of biceps brachii MU's have been recorded during voluntary static contraction followed without any break by dynamic contraction. The MU's activity was recorded by means of wire-electrodes.
From 45 tests carried out on 15 normal subjects in which 78 MU's were studied it has been found that: (1) the same MU may discharge both in static and in dynamic work; (2) in both types of work the MU's firing rate and recruitment only depend on the external force. For example, a single MU which does not discharge for a given level of static force will discharge during the following dynamic work, but can also be recruited for a higher level of static force.
Thus, it can be said that the qualification “tonic” and “phasic”, characterize the MU's twitches and do not imply any static-dynamic differentiation.
A comparison has been made between the patterns of MU activity which occur in movement against load and those which have been found in movement against inertia. It is suggested that while the latter are preprogrammed, the former fall under a feed-back control.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Bouisset, S., Maton, B.: The quantitative relation between surface and intramuscular electromyographic activities for voluntary movement. Am. J. Phys. Med. 51, 285–295 (1972)
Bouisset, S.: EMG and muscle force in normal motor activities. In: New developments in electromyography and clinical neurophysiology, Vol. 1, Desmedt, J. E. (ed.), pp. 547–583. Basel: Karger 1973
Buchthal, F., Schmalbruch, H.: Contraction times and fibre types in intact human muscle. Acta Physiol. Scand. 79, 435–452 (1970)
Burke, R. E.: Firing patterns of gastrocnemius motor units in the decerebrate cat. J. Physiol. (Lond.) 196, 631–654 (1968)
Burke, R. E., Levine, D. N., Tsairis, P., Zajac, F. E.: Physiological types and histochemical profiles in motor units of the cat gastrocnemius, J. Physiol. (Lond.) 234, 723–748 (1973)
Close, R. J.: Dynamic properties of skeletal muscles. Physiol. Rev. 52, 129–197 (1972)
Engel, W. K.: The essentiality of histo- and cytochemical studies of skeletal muscle in the investigation of neuromuscular disease. Neurology 12, 778–794 (1962)
Gollnick, P. D., Piehl, K., Saltin, B.: Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity and at varying pedalling rates. J. Physiol. (Lond.) 241, 45–57 (1974)
Granit, R., Phillips, C. T., Skoglund, S., Steg, G.: Differentiation of tonic from phasic alpha ventral horn cells by strech, pinna and crossed extensor reflexes. J. Neurophysiol. 20, 470–481 (1957)
Gydikov, A., Kosarov, D.: Some features of different motor units in human biceps brachii. Pflügers Arch. 347, 75–88 (1974)
Harris, D. A., Henneman, E.: Identification of two species of alpha motoneurons in cat's plantaris pool. J. Neurophysiol. 40, 16–25 (1977)
Henneman, E., Olson, C. B.: Relations between structure and function in the design of skeletal muscles. J. Neurophysiol. 28, 581–598 (1965)
Hilaire, G., Monteau, R., Dussardier, M.: Modalités du recrutement des motoneurones phréniques. J. Physiol. (Paris) 64, 457–478 (1972)
Kernell, D.: The adaptation and the relation between discharge frequency and current strength of cat lumbosacral motoneurones stimulated by long-lasting injected currents. Acta Physiol. Scand. 65, 65–73 (1965)
Kernell, D.: Input resistance, electrical excitability, and size of ventral horn cells in cat spinal cord. Science 152, 1637–1640 (1966)
Maton, B., Bouisset, S.: Motor unit activity and preprogramming of movement in man. Electroencephalogr. Clin. Neurophysiol. 38, 658–660 (1975)
Maton, B.: Motor unit differenciation and integrated surface EMG in voluntary isometric contraction. Eur. J. Appl. Physiol. 35, 149–157 (1976)
Maton, B.: Fréquence et recrutement des unités motrices du muscle biceps brachial au cours du travail statique chez l'homme normal. J. Physiol. (Paris) 73, 177–199 (1977)
Milner-Brown, H. S., Stein, R. B., Yemm, R.: The orderly rectruitment of human motor units during voluntary isometric contractions. J. Physiol. (Lond.) 230, 359–370 (1973)
Mishelevich, D. J.: Repetitive firing to current in cat motoneurons as a function of muscle unit twitch type. Exp. Neurol. 25, 401–409 (1969)
Somjen, G. G., Carpentier, D. O., Henneman, E.: Responses of motoneurons of different sizes to graded stimulation of supraspinal centers of the brain. J. Neurophysiol. 28, 958 (1965)
Warmolts, J. B., Engel, W. K.: Correlation of motor-unit behavior with histochemical myofiber type in humans by open-biopsy electromyography. Trans. Am. Neurol. Assoc. 96, 5 (1972)
Warmolts, J. R., Engel, W. K.: Correlation of motor unit behavior with histochemical myofiber type in humans by open-biopsy electromyography. In: New developments in electromyography and clinical neurophysiology, Vol. 1, Desmedt, J. E. (ed.), pp. 35–40. Basel: Karger 1973
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Maton, B. Fast and slow motor units: Their recruitment for tonic and phasic contraction in normal man. Europ. J. Appl. Physiol. 43, 45–55 (1980). https://doi.org/10.1007/BF00421355
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00421355