High but not moderate-intensity endurance training increases pain tolerance: a randomised trial

To examine the effect of high-intensity interval training (HIIT) compared to volume-matched moderate-intensity continuous training (CONT) on muscle pain tolerance and high-intensity exercise tolerance. Twenty healthy adults were randomly assigned (1:1) to either 6 weeks of HIIT [6-8 x 5 min at halfway between lactate threshold and maximal oxygen uptake (50%Delta)] or volume-matched CONT (similar to 60-80 min at 90% lactate threshold) on a cycle ergometer. A tourniquet test to examine muscle pain tolerance and two time to exhaustion (TTE) trials at 50%Delta to examine exercise tolerance were completed pre- and post-training; the post-training TTE trials were completed at the pre-training 50%Delta (same absolute-intensity) and the post-training 50%Delta (same relative-intensity). HIIT and CONT resulted in similar improvements in markers of aerobic fitness (all P ae 0.081). HIIT increased TTE at the same absolute- and relative-intensity as pre-training (148 and 43%, respectively) to a greater extent than CONT (38 and -4%, respectively) (both P ae 0.019). HIIT increased pain tolerance (41%, P < 0.001), whereas CONT had no effect (-3%, P = 0.720). Changes in pain tolerance demonstrated positive relationships with changes in TTE at the same absolute- (r = 0.44, P = 0.027) and relative-intensity (r = 0.51, P = 0.011) as pre-training. The repeated exposure to a high-intensity training stimulus increases muscle pain tolerance, which is independent of the improvements in aerobic fitness induced by endurance training, and may contribute to the increase in high-intensity exercise tolerance following HIIT.