Neural mechanisms of pain processing differ between endurance athletes and nonathletes: A functional connectivity magnetic resonance imaging study

Pain perception and the ability to modulate arising pain vary tremendously between individuals. It has been shown that endurance athletes possess higher pain tolerance thresholds and a greater effect of conditioned pain modulation than nonathletes, both indicating a more efficient system of endogenous pain inhibition. The aim of the present study was to focus on the neural mechanisms of pain processing in endurance athletes that have not been investigated yet. Therefore, we analyzed the pain processing of 18 male athletes and 19 healthy male nonathletes using functional magnetic resonance imaging. We found lower pain ratings in endurance athletes compared to nonathletes to physically identical painful stimulation. Furthermore, brain activations of athletes versus nonathletes during painful heat stimulation revealed reduced activation in several brain regions that are typically activated by nociceptive stimulation. This included the thalamus, primary and secondary somatosensory cortex, insula, anterior cingulate cortex, midcingulate cortex, dorsolateral prefrontal cortex, and brain stem (BS). Functional connectivity analyses revealed stronger network during painful heat stimulation in athletes between the analyzed brain regions except for connections with the BS that showed reduced functional connectivity in athletes. Post hoc correlation analyses revealed associations of the subject's fitness level and the brain activation strengths, subject's fitness level and functional connectivity, and brain activation strengths and functional connectivity. Together, our results demonstrate for the first time that endurance athletes do not only differ in behavioral variables compared to nonathletes, but also in the neural processing of pain elicited by noxious heat.