Recruitment and de-recruitment thresholds of motor units in the wrist extensor muscles can undergo important random fluctuations, even when they are measured during stereotyped contractions and relaxations. These fluctuations were statistically quantified and compared. The statistical analysis indicated that recruitment and de-recruitment thresholds display the same kind of fluctuations, and that the successive measurements are randomly distributed following a quasi-normal law. We suggest that the notion of force threshold for motor unit recruitment and de-recruitment might be oversimplified and that a motor unit seems to have a range of force in which it can be recruited or de-recruited. Comparison of the mean values of recruitment and de-recruitment thresholds of the motor units in the extensor carpi radialis muscles showed that de-recruitment thresholds were significantly lower than recruitment thresholds. This difference in the thresholds, together with the difference in the motor unit discharge frequency during a contraction and a relaxation, suggests a differential control of the motoneurone activity during contractions and relaxations.
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Büdingen HJ, Freund HJ (1976) The relationship between the rate of rise of isometric tension and motor unit recruitment in a human forearm muscle. Pflugers Arch 362:61–67
DeLuca CJ, LeFever RS, McCue MP, Xenakis AP (1982) Behaviour of human motor units in different muscles during linearly varying contractions. J Physiol (Lond) 329:113–128
Denier van der Gon JJ, ter Haar Romeny BM, van Zuylen EJ (1985) Behaviour of motor units of human arm muscles: differences between slow isometric contraction and relaxation. J Physiol (Lond) 359:107–118
Freund HJ (1983) Motor unit and muscle activity in voluntary motor control. Physiol Rev 63:387–436
Garnett R, Stephens JA (1980) The reflex responses of single motor units in human first dorsal interosseous muscle following cutaneous afferent stimulation. J Physiol (Lond) 303:351–364
Garnett R, Stephens JA (1981) Changes in the recruitment threshold of motor units produced by cutaneous stimulation in man. J Physiol (Lond) 311:351–364
Grimby L, Hannerz J (1968) Recruitment order of motor units in voluntary contraction: changes induced by proprioceptive afferent activity. J Neurol Neurosurg Psychiatry 31:565–573
Grimby L, Hannerz J (1974) Differences in recruitment order and discharge pattern of motor units in the early and late flexion reflex components in man. Acta Physiol Scand 90:555–564
Milner-Brown HS, Stein RB, Yemm R (1973) The orderly recruitment of human motor units during voluntary isometric contractions. J Physiol (Lond) 230:350–370
Person RS (1974) Rhythmic activity of a group of human motoneurones during voluntary contraction of a muscle. Electroencephalogr Clin Neurophysiol 36:585–595
Person RS, Kudina LP (1972) Discharge frequency and discharge pattern of human motor units during voluntary contraction of muscle. Electroencephalogr Clin Neurophysiol 32:471–483
Romaiguère P, Vedel JP, Pagni S (1989a) Fluctuations in motor unit recruitment threshold during slow isometric contractions of wrist extensor muscles in man. Neurosci Lett 103:50–55
Romaiguère P, Vedel JP, Pagni S, Zenatti A (1989b) Physiological properties of motor units of the wrist extensor muscles in man. Exp Brain Res 78:51–61
Tanji J, Kato M (1973) Recruitment of motor units in voluntary contraction of a finger muscle in man. Exp Neurol 40:759–770
Thomas JS, Schmidt EM, Hambrecht FT (1978) Facility of motor unit control during tasks defined directly in terms of unit behaviors. Exp Neurol 59:384–395
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Romaiguère, P., Vedel, J. & Pagni, S. Comparison of fluctuations of motor unit recruitment and de-recruitment thresholds in man. Exp Brain Res 95, 517–522 (1993). https://doi.org/10.1007/BF00227145
- Motor units
- Recruitment threshold
- De-recruitment threshold