Bimodal relationship of human tremor and shivering on introduction to cold exposure

Four subjects were exposed to an environmental challenge of -12 degrees C for 15 min in four conditions of exposure: 1) clothed body and clothed arm, 0.5 clo units: 2) clothed body and exposed arm, 0.4 col; 3) exposed body and exposed arm, 0.1 clo: 4) exposed body and clothed arm, 0.2 clo. Core temperature, surface temperature of the right arm, perceived thermal comfort, EMG indicated onset of shivering, and the frequency of tremor using accelerometry were monitored and data collected every 30 s. The results indicate that tremor frequency significantly increases with cold exposure, but that a significant drop in tremor frequency precedes the onset of shivering. It is suggested that pre-shivering tetany occurs prior to the onset of shivering, acts as a load upon the lever of the hand and reduces the oscillation of the limb.