Abstract
When voluntary muscles are put under tension against resistance through conscious effort, and then allowed to relax with the resistance removed, there follows an involuntary contraction in the original direction. Thus, as has long been known, if one stands against a wall, pushing the hand strongly against it, with the arm held stiff, on stepping away from the wall, the arm slowly rises toward a horizontal position. This phenomenon, which may be called after-contraction, has been studied by Kohnstamm, Csiky and others, who have given various explanations of its mechanism, none of which, however, seems adequate. In view of the more recent advances in the physiology of the nervous system, it seemed to us that further study of the after-contraction would be of value. The present report deals with some aspects of the reaction.
The after-contraction may be obtained from any voluntary muscle group, and in these experiments the movement studied was flexion at the hip joint, the leg being extended. The subject stood on a platform, supporting his weight on one foot. To the other foot, hanging free, was attached a cord, passing over a pulley and carrying a fixed weight. Also attached to this foot was a string connected with a system of levers arranged to record the leg movement on a kymograph. At a given signal, the subject lifted the weight off its support by raising the extremity, and held it in a fixed position for a definite period. Then, at a second signal, the leg was relaxed and the weight disconnected. After a variable latent period the leg slowly rises, without conscious effort on the part of the subject and, indeed, somewhat to his astonishment.
Get full access to this article
View all access options for this article.