Intensity thresholds for aerobic exercise-induced hypoalgesia.

INTRODUCTION: Despite many studies investigating exercise-induced hypoalgesia, there is limited understanding of the optimal intensity of aerobic exercise in producing hypoalgesic effects across different types of pain stimuli. Given that not all individuals are willing or capable of engaging in high-intensity aerobic exercise, whether moderate-intensity aerobic exercise (MAE) is associated with a hypoalgesic response and whether this response generalizes to multiple pain induction techniques needs to be substantiated.
PURPOSE: This study's purpose is to test for differences in the magnitude of pressure and heat pain modulation induced by MAE and vigorous-intensity aerobic exercise (VAE).
METHODS: Twelve healthy young males and 15 females completed one training session and three testing sessions consisting of 25 min of 1) stationary cycling at 70% HR reserve, 2) stationary cycling at 50% HR reserve, or 3) quiet rest (control). Pain testing was conducted on both forearms before and immediately after each condition and included the following tests: pressure pain thresholds, suprathreshold pressure pain test, static continuous heat test, and repetitive pulse heat pain test. Repeated-measures ANOVA was conducted on each pain measure.
RESULTS: VAE and MAE reduced pain ratings during static continuous heat stimuli and repetitive heat pulse stimuli, with VAE producing larger effects. VAE also increased pressure pain thresholds, whereas neither exercise influenced suprathreshold pressure pain ratings.
CONCLUSION: These results suggest that MAE is capable of producing a hypoalgesic effect using continuous and repetitive pulse heat stimuli. However, a dose-response effect was evident as VAE produced larger effects than MAE.