The purpose of this study was to examine the effects of anticipated task duration on ratings of perceived exertion during treadmill running. Male subjects.(N = 15) completed two separate runs on a motor-driven treadmill at 85% V02 max. During one trial, subjects ran for a period of 20 minutes, while for a second trial, subjects were led to believe that they would be running for 30 minutes. In each case, the trials were terminated at the 20-minute mark. Ratings of perceived exertion, heart rates, respiratory rates, and ventilatory minute volumes were collected across each trial. Results supported the supposition that the anticipation of continued performance mediated ratings of effort expenditure. This effect was obtained only during moderate work levels and was in contrast to research examining mental fatigue.