Changes in Heart Rate, Muscle Activity, and Anxiety Level Following Shock Threat

Variations in HR, forearm EMG, and anxiety level were recorded over a 6-min interval scheduled to end with an electric shock. Sixty subjects were divided equally among four groups. Only two of the groups could watch a clock while waiting for the shock; the other two had no clock available. One group in each of these two conditions gave verbal reports of anxiety at various times while waiting for the shock. The results showed an increase in HR at the end of the anticipation interval in the two Clock groups, and no such rise in the two No Clock groups. Very similar results were found for anxiety level, but not for forearm EMG. These findings suggest that HR increases during anticipation of shock reflect a rising anxiety level, rather than a concomitant increase in muscle activity.