During physical exercise, individuals have access to internal sensory and external environmental cues that compete for attentional focus. Two experiments examined when attention to external cues attenuates the perception of physical symptoms and fatigue. In Experiment 1, subjects' physical performance was held constant during exercise on a treadmill. Subjects hearing distracting sounds reported less fatigue and fewer symptoms than subjects hearing an amplification of their own breathing. In Experiment 2, subjects jogging equal length cross-country and lap courses evinced faster times on the former, where increased external attention was necessary. Self-reports of symptoms and fatigue, however, were comparable on the two courses. The results are interpreted in terms of attentional focus shifting from one information source to another as needed, with attention to any one source diminishing attention to others.