A variety of physiological responses, classified as local or central factors, have been suggested as providing the primary input for perception of effort during exercise. The potency of these responses as perceptual cues, however, has seldom been addressed in terms of relevant modifying variables such as exercise intensity, exercise duration, exercise modality, and steady-state vs progressive exercise. This paper provides a critical review of the most relevant perceived exertion literature in terms of these considerations. It has been proposed that the impact of physiological responses as perceptual cues is dependent on their availability to conscious monitoring during exercise. The viability of this suggestion as a criterion for determining the importance of local and central cues for perceived exertion is also examined.