Physical activity does not account for the physiological response to forced swim testing.

Two experiments were conducted to examine physiological variables associated with the immobility response in the forced swim test. The first study compared the effects of water immersion, treadmill running, and foot shock, and showed that the time-related pattern of reactions to these three conditions, especially those involving lactate, glucose, anion gap (a measure of metabolic acidosis), and carbon dioxide differed significantly. The second study examined the role of food deprivation, and showed that this manipulation does not affect the behavior or physiological response of rats to testing. These results indicate that the physiological changes occurring during the forced swim are not simply due to increased physical activity or stress.