The effect of exercise intensity on exercise-induced hypoalgesia in cancer survivors: A randomized crossover trial.

Pain is experienced by people with cancer during treatment and in survivorship. Exercise can have an acute hypoalgesic effect (exercise-induced hypoalgesia; EIH) in healthy individuals and some chronic pain states. However, EIH, and the moderating effect of exercise intensity, has not been investigated in cancer survivors. This study examined the effect of low- and high-intensity aerobic exercise on EIH in cancer survivors after a single exercise session as well as a brief period of exercise training (2-weeks, three exercise sessions per week). Participants (N = 19) were randomized to low- (30%-40% Heart Rate Reserve (HRR) or high- (60%-70% HRR) intensity stationary cycling for 15-20 min. Pressure pain thresholds (PPT) were assessed over the rectus femoris and biceps brachii before and after a single exercise session and again after a short training period at the assigned intensity. Then, following a 6-week washout period, the intervention was repeated at the other intensity. After the first exercise session, high-intensity exercise resulted in greater EIH over the rectus femoris than low intensity (mean difference ± SE: -0.51 kg/cm2  ± 0.15, Cohen's d = 0.78, p = 0.004). After a 2-week training period, we found no difference in EIH between intensities (0.01 kg/cm2  ± 0.25, d = 0.00 p = 0.99), with comparable moderate effect sizes for both low- and high-intensity exercise, indicative of EIH. No EIH was observed over the biceps brachii of the arm at either low or high intensity. Low-intensity exercise training may be a feasible option to increase pain thresholds in cancer survivors.