Background and aims: Exercise reduces pain sensitivity in pain-free subjects known as exercise-induced hypoalgesia (EIH). Positive information about EIH increases EIH expectations and the hypoalgesic response after exercise. It is currently unknown how negative information influences the subsequent hypoalgesic response, which may be more relevant in understanding the lack of EIH in some patients with chronic pain. Thus, the aim of the study was to investigate how positive and negative information about the effect of exercise influence EIH expectations and the hypoalgesic response.
Methods: In a randomized, double blind study, 83 pain-free subjects were randomized to one of three groups receiving different information about EIH: a neutral- information group, a hypoalgesia-information group and a hyperalgesia-information group. Pain sensitivity was assessed with pressure pain threshold (PPT) at the thigh before and after a 3 min isometric wall-squat exercise. Subjects were also asked to rate how they had expected the wall-squat exercise to affect PPT prior to performing the exercise.
Results: Expectations about the effect of wall-squat on PPT as well as the hypoalgesic response after exercise was significantly different between groups (Fig. 1) with a larger response in the hypoalgesic expectancy group, but hyperalgesia in the hyperalgesic expectancy group (P<0.05). Moreover, there was a significant positive association between the increase in PPT and positive expectations (r=0.35, P=0.001).
Conclusions: The hypoalgesic effect after isometric exercise was influenced by the information given prior to the exercise. Negative information completely abolished the hypoalgesic response after exercise likely mediated by negative expectations.

THE INFLUENCE OF INFORMATION ON THE HYPOALGESIC EFFECTS OF EXERCISE - A RANDOMIZED CONTROLLED DOUBLE-BLIND STUDY