A test of exercise analgesia using signal detection theory and a within-subjects design.

Evidence for the existence of exercise-induced analgesia has been weak, inconsistent, or anecdotal. The present study addresses criticisms of previous research by using a signal-detection analysis of pain perception in a within-subjects, repeated-measures research design with 22 endurance athletes who exercised in a naturalistic setting. Analysis showed discriminability measures from the lower intensities of a radiant-heat pain-perception task were significantly lower after exercise than the subjects' discriminability after a no-exercise period. This is consistent with discriminability decreases seen in studies of subjects who are under the influence of analgesic chemicals such as morphine and nitrous oxide. Discriminability differences were not seen in this study at the higher intensities of the stimulus, suggesting that exercise generates perceptual changes that may not reach pain-mediating levels. Visual analogue data suggest cognitive and motivational factors also play a role in report of pain after exercise.