Effects of physical activity on initial level and response magnitude: an experimental study of the LIV

Two exercise and two relaxation conditions were used to manipulate subjects' overall level of physical activity. A digit-transformation-and-recall task was administered under each of these four conditions in order to elicit physiological responses. Measures of prestimulus level and response magnitude were taken for each of six dependent variables: skin conductance (SC), heart rate (HR), finger pulse volume (PV), and three respiration indices. It was hypothesized that as the subject's degree of activity increased the physiological variables would show ergotropic changes in prestimulus level together with decreasing magnitudes of response to the digit task. The results provided a reasonable degree of support for these predictions. Evidence for concomitant changes in prestimulus level and response magnitude was consistent with Wilder's Law of Intial Value (LIV). There were some cases, however, where response magnitude showed a predicted effect of treatment in the absence of a difference in prestimulus level; these findings could not be explained by the traditional LIV model.