Abstract
The results and uncertainties of histological methods of determining the numbers of motor units in various human muscles are reviewed. An electrophysiological technique employing graded nerve stimulation is also described and the underlying assumptions are pointed out; the technique depends on comparing the sizes of individual motor unit potentials with that of the maximal muscle response. The electrophysiologically-derived values for the extensor digitorum brevis (EDB), thenar, hypothenar and soleus muscles are reported for healthy subjects below the age of 60. Beyond the age of 60, there is a progressive loss of functioning motor units which has been attributed to motoneurone failure. The sizes of the motor units have been assessed in terms of the evoked potential amplitudes and twitch tension of individual motor units; both methods indicate that there is a considerable variation in this parameter. Attention is drawn to the marked spurt in contractile force which affects motor units in males at puberty. Finally, an attempt has been made to determine the proportions of motor units with ‘fast’ and ‘slow’ twitches within various human muscles and possible correlations with results of histochemical staining have been sought.
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McComas, A.J., Sica, R.E.P., Upton, A.R.M., Longmire, D., Caccia, M.R. (1973). Physiological Estimates of the Numbers and Sizes of Motor Units in Man. In: Stein, R.B., Pearson, K.G., Smith, R.S., Redford, J.B. (eds) Control of Posture and Locomotion. Advances in Behavioral Biology, vol 7. Springer, Boston, MA. https://doi.org/10.1007/978-1-4613-4547-3_5
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DOI: https://doi.org/10.1007/978-1-4613-4547-3_5
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