Study of the Mechanisms of Action of the Hypoalgesic Effect of Pressure Under Shock Waves Application: A Randomised Controlled Trial

Objective: To determine if the perceived pain intensity during the application of shock waves (SWs) is a determinant mechanism in producing hypoalgesic changes in pressure pain thresholds (PPTs) in asymptomatic individuals.

Design: A randomised, single-blind controlled trial [NCT03455933].

Setting: University.

Participants: Sixty-three asymptomatic individuals.

Interventions: Participants were randomised into three groups: 1-SWs causing mild pain (SW-DP); 2-SWs generating moderate pain (SW-MP); and 3-cold pressor test (CPT).

Main Outcome Measurements: Before and after the intervention, the PPT was evaluated bilaterally at the following points: lateral epicondyle, median nerve in the flexure of the elbow, and tibia.

Results: The results showed differences between various groups over time for all PPTs assessments, due to the existence of statistically significant differences in the interaction group x times (dominant arm lateral epicondyle [P < 0.001; ηp = 0.255]; dominant arm median nerve [P = 0.001; ηp = 0.212]; nondominant arm lateral epicondyle [P < 0.001; ηp = 0.275]; nondominant arm median nerve [P < 0.001; ηp = 0.268]; tibia [P = 0.012, ηp = 0.138]). The SW-MP group obtained a significant increase in all the PPT evaluations compared with the SW-DP group (d > 0.80). The CPT group only showed significantly higher results, and of high magnitude (d > 0.80), regarding the SW-DP group for the PPT evaluation in the dominant member. The SW-MP group showed differences compared with the CPT only for the PPT obtained in the nondominant arm.

Conclusions: The findings show that SW treatment generates a hypoalgesic effect on the application point, with moderate pain. Further studies are necessary in order to link these hypoalgesic changes to the activation of the descending inhibitory systems.