Abstract A line-matching test was given to 15 female subjects while exercising on a motor-driven treadmill. The accuracy and speed of each subject were recorded for four 3-min stages of exercise: stage 1, 0.7 m s−1 at 10% gradient; stage 2, 1.1 m s−1 at 12% gradient; stage 3, 1.52 m s−1 at 14% gradient; stage 4, 1.88 ms−1 at 16% gradient. Heart rate was recorded for each subject continually throughout the test. Increased levels of concomitant exercise had no significant effect on accuracy of performance and did not produce increased speed of mental performance, except in the last stage of exercise which differed significantly from the first three stages. Speed of performance in the post-test was also significantly greater than it was in the first three stages of exercise.