Abstract
The researches of Lapicque and Bourguignon have shown that the excitability of muscles as measured by their chronaxie is closely associated with the form and duration of their contraction, the general rule being that the slower the contraction the longer the chronaxie and vice versa. This has been attested, on the one hand, by the comparatively long chronaxies of smooth as compared with striated musculature (animals) and on the other hand, by the chronaxie changes following nerve degeneration and those met with in the various muscular dystrophies.
In view of this association it seemed to us that there might be some correlation between motor speed and neuromuscular excitability, which might account for differences in speed of movement, on the basis of a constitutional (organic) factor. The present note is a report on the results obtained by simultaneous measurement of the chronaxie and reaction time in 20 normal human subjects.
In obtaining the chronaxie we followed Bourguignon's technique, employing a method described by us in a previous paper, 1 with the apparatus assembled into a simple portable form devised by one of us. The chronaxie was taken over the motor point of the biceps muscle. The average of five readings was .taken as the chronaxie.
The speed of bicepital contraction against which we correlated the muscle chronaxie was obtained as follows: Each subject after placing his forearm, fist clenched, upon a table in front of him was instructed, upon a given signal, to move his fist horizontally to the right (a distance of six inches), strike a key and then flex his arm as quickly as possible in a vertical direction. The height and distance through which the subject could flex his arm was limited by an extended board fastened 12 inches above the surface of the table and parallel to it, on the under surface of which was attached a legless telegraph key against which the subject's fist inevitably struck.
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