The Kohnstamm Phenomenon: Involuntary Movement Followed by Sustained Muscle Contraction

Rafael Serra, Sierra Cardi

rserra@unca.edu

BIOLOGY

The Kohnstamm phenomenon, a lightness sensation of the limbs and involuntary movement following sustained muscle contraction, is well documented to occur. However, the physiological mechanisms behind this phenomenon are not well understood. This study investigates this phenomenon from the perspective of the muscles involved and the peripheral nervous system. This research examines the effect of shoulder position, muscle activation, external loading, hand position, and external electrical stimulation on the Kohnstamm phenomenon. We documented the presence and intensity of the Kohnstamm phenomenon from a sample of UNCA student volunteers by having subjects press against wooden stands with force plates attached, which allowed us to measure the force of the contraction of the shoulder muscles at two different widths (1 m and 1.25 m). We also used EMG to record the electrical activity of the deltoid and supraspinatus muscles for a subset of people in the study. Of the 39 subjects we tested, 33 experienced the phenomenon and 6 did not. For the majority of subjects who did experience the phenomenon, about 79% reported that the effect was greater when pressing against the narrower frame width. External loading (having the subject hold a weight in one hand) and applying an external stimulus with a TENS unit both had varying effects on the subjects’ perceived intensity of the phenomenon. Although the deltoid is often attributed as the primary muscle involved with the Kohnstamm phenomenon, our initial results suggest that the effect is largely due to proprioception involving the deeper shoulder muscles of the rotator cuff.

May-16-2024