The effect of a change in body weight on running and responding reinforced by the opportunity to run

Previous research has shown that running increases as body weight decreases. One interpretation of this relationship is that motivation to run increases as body weight decreases. In the present study, the relationships among body weight, running, and responding for the opportunity to run were investigated. Fourteen male Wistar rats were trained to respond on levers. The reinforcing consequence was the opportunity to run for 60 seconds. in each session, subjects were exposed to a series of variable-interval schedules. Over sessions, body weight was increased from 80% to 100% of an initial ad-rib level and then returned to 80%. Results showed that running and lever-pressing rates were lower at the higher body weight whereas mean latency to respond following reinforcement was higher at the higher body weight. Analysis of between subjects data also revealed orderly relationships. At each body weight, lever-pressing rates were positively related to running rates. In addition, changes in running caused by change in body weight were positively related to changes in lever-pressing rates and negatively related to changes in latency Finally, changes in running were not related to initial levels of running. In sum, the results were consistent with the interpretation that motivation to run varies with body weight.