Intensity and duration threshold for aerobic exercise-induced analgesia to pressure pain.

Objective: To examine how exercise-induced analgesia is affected by the duration and intensity of aerobic exercise.

Design: Repeated-measures design.

Setting: Exercise science laboratory.

Participants: Convenience sample of 12 healthy male and female volunteers (mean age +/- standard deviation, 32+/-9 y).

Interventions: Pain ratings were assessed before and at 5 and 30 minutes after treadmill exercise of 10 minutes at 75% maximal oxygen uptake (Vo(2)max), 30 minutes at 50% Vo(2)max, and 30 minutes at 75% Vo(2)max (randomized order and no less than 48 h between each bout).

Main Outcome Measures: Pain ratings were measured on a visual analog scale at 10-second intervals during a 2-minute pressure-pain stimulus to the nondominant index finger.

Results: Pain ratings were significantly decreased (P<.05) from pre-exercise values 5 minutes after 30 minutes of exercise at 75% Vo(2)max but returned toward baseline by 30 minutes after exercise. There were no significant changes in pain ratings after 10 minutes of exercise or after exercise at 50% Vo(2)max.

Conclusions: There are thresholds for both the intensity (>50% Vo(2)max) and duration (>10 min) of exercise required to elicit exercise analgesia.