Learning To Suffer: High- But Not Moderate-intensity Training Increases Pain Tolerance: Results From A Randomised Study

PURPOSE: To compare the effect of volume-matched high-intensity interval training (HIIT) and moderate-intensity continuous training (CONT) on ischaemic muscle pain tolerance and high-intensity exercise tolerance. METHODS: Twenty healthy adults were randomly assigned to either 6 weeks of HIIT (6-8 x 5 min at halfway between lactate threshold and maximal oxygen uptake [50%Δ]) or volume-matched CONT (~60–80 min at 90% lactate threshold) on a cycle ergometer. Immediately pre- and post-training, participants completed a tourniquet test to examine ischaemic muscle pain tolerance and two time to exhaustion (TTE) trials at 50%Δ to examine exercise tolerance; the post-training TTE trials were completed at the pre-training 50%Δ (same absolute intensity) and the post-training 50%Δ (same relative intensity). RESULTS: HIIT and CONT resulted in similar improvements in all markers of aerobic fitness (P>0.05). Compared with pre-training, 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) (P<0.05). HIIT increased pain tolerance (41%, P<0.001), which demonstrated moderate non-significant associations with the increase in TTE at the same relative intensity as pre-training (r=0.50, P=0.07), however pain tolerance was unaffected by CONT (-3%, P>0.05). CONCLUSION: The repeated exposure to a high-intensity noxious exercise training stimuli increases ischemic muscle pain tolerance, which is independent of the improvements in aerobic fitness induced by endurance training. This increase in ischemic muscle pain tolerance may be an important contributor to the increase in highintensity exercise tolerance following HIIT.