Abstract.Perceived exertion was measured using a linear grading scale, in three healthy males performing paired patterns of continuous and intermittent exercise with the same average power output. Intermittent exercise with work periods of 10 sec. alternating with recovery periods of loadless pedalling for 30 sec. was associated with lower perceived exertion grades than when work periods were 30 or 120 sec. Perceived exertion, oxygen intake, ventilation, heart rate, and blood lactate concentration were all significantly higher for intermittent exercise than for continuous exercise with the same average power output. The relationships between perceived exertion and the physiological variables was the same for the two forms of exercise despite widely different mechanical stresses on the legs. Mechanical factors were therefore thought to make a relatively unimportant contribution to perceived exertion over the range of exercise intensities studied.—The high degree of correlation between perceived exertion and the measured physiological variables suggests a wider use of exertion grading in field studie