Exercise and pain sensitivity in healthy adults: the influence of aerobic capacity and chronic aerobic training

Exercise-induced hypoalgesia refers to the reduction in pain sensitivity that occurs with exercise. This phenomenon is well documented following acute exercise, but less is known of the influence of chronic exercise training on pain sensitivity in healthy adults. Further, the mechanisms that modulate pain sensitivity following exercise are also unclear. Two studies were designed to investigate these issues and a third study was designed to investigate the reliability of the methods of pain assessment used in this research. The initial study examining the reliability of measuring pressure pain threshold and ischaemic pain tolerance used algometry and a tourniquet test on 3 occasions over non-consecutive days. For pressure pain threshold, reliability was also assessed using different raters and at different anatomical sites. The second study examined the relation between aerobic capacity and pain sensitivity in a cross-sectional sample. Participants pressure pain threshold and ischaemic pain tolerance was assessed, and they also performed a maximal aerobic test. The relation between aerobic capacity and pain sensitivity was then calculated. The final study examined the effect of 6 weeks of moderate-high intensity aerobic cycle exercise training on pain sensitivity. Participants were assessed for pain sensitivity and aerobic capacity, as well as physical activity and mood, and then allocated to an exercise or control group. The exercise group performed 6 weeks of aerobic cycle exercise, 3 times per week for 30 min at 75% of their maximal aerobic capacity. The control group maintained their usual level of physical activity throughout the 6 week intervention. Participants were then re-assessed following the 6 week intervention period. Results of these studies indicate that: 1) the pressure and ischaemic methods pain assessment methods were reliable across days and between raters; 2) aerobic capacity is unrelated to pain sensitivity in healthy adults, and 3) moderate-high intensity chronic aerobic exercise training increases pain tolerance in healthy adults. In conclusion, exercise training is capable of increasing pain tolerance, but not pain threshold, and the effect of exercise on pain sensitivity does not appear to be modulated by aerobic capacity