Exercise increases pressure pain thresholds (PPT) in pain-free individuals, known as exercise-induced hypoalgesia (EIH). Positive pre-exercise information can elicit higher EIH responses, but the effect of positive versus negative pre-exercise information on EIH is unknown. The primary aim of this randomized controlled trial (RCT) was to compare EIH at the exercising thigh muscle following an isometric squat exercise between individuals receiving positive versus negative pre-exercise information about the effect of exercise on pain. Secondary aims were to compare EIH at non-exercising muscles between groups, and to investigate the relationship between participants’ expectations and EIH.
Eighty-three participants were randomly assigned to brief positive (n=28), neutral (n=28) or negative (n=27) verbal information. The neutral information group was included in the study as a reference group. PPTs at the thigh and trapezius muscles were assessed before and after the intervention (i.e. pre-exercise information+squat exercise). Expectations of pain relief were assessed using a numerical rating scale (-10 (most negative) to 10 (most positive)).
Change in quadriceps and trapezius PPTs after the squat exercise showed a large difference between the positive and negative information groups (Quadriceps: 102 kPa 95% CI: 55 to 150; effect size: 1.2; Trapezius: 41 kPa 95 % CI: 16 to 65; effect size: 0.9). The positive information group had a 22% increase in quadriceps PPT whereas the negative information group had a 4% decrease. A positive correlation was found between expectations and increase in PPT.
Negative pre-exercise information caused hyperalgesia after the wall squat exercise whereas positive or neutral pre-exercise information caused hypoalgesia. Positive pre-exercise information did not change the magnitude of EIH compared to neutral information.