Methods for the quantitative study of human muscle tonus have been developed along two different lines: 1. Several mechanisms have been designed to give a measurement of the resistance of muscles to pressure on the muscle bellies. There can be little doubt that there is a certain correlation between the hardness of muscles and their ability to resist a stretching pull, but tonus is usually thought of in terms of resistance to stretch so that these methods are obviously indirect unless one defines tonus to mean muscle hardness. At any rate, studies of this sort appear, on the face of them, subject to considerable error because of the necessity of considering the compressibility of extraneous tissues involved in the measurements. No one appears to have followed these methods long enough to have presented a searching analysis of normal muscle compressibility.
2. Several writers have published descriptions of machines with which
McKINLEY JC, BERKWITZ NJ. QUANTITATIVE STUDIES ON HUMAN MUSCLE TONUS: I. DESCRIPTION OF METHODS. Arch NeurPsych. 1928;19(6):1036–1056. doi:10.1001/archneurpsyc.1928.02210120069007
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