Abstract
Exercise might lead to a release of endogenous opioids, potentially resulting in pain relief. However, the neurobiological underpinnings of this effect remain unclear. Using a pharmacological within-subject fMRI study with the opioid antagonist naloxone and different levels of aerobic exercise and pain we investigated exercise-induced hypoalgesia (N = 39, 21 female). Overall, we were unable to detect reduced pain after high-intensity aerobic exercise as compared to low-intensity aerobic exercise. Accordingly, we observed no significant changes in the descending pain modulatory system. The µ-opioid antagonist naloxone significantly increased overall pain ratings but showed no interaction with exercise intensity. An exploratory analysis suggested an influence of fitness level and sex where males showed greater hypoalgesia after high-intensity exercise with increasing fitness levels. This effect was attenuated by naloxone and mirrored by fMRI signal changes in the medial frontal cortex, where activation also varied with fitness level and sex, and was reversed by naloxone. These results indicate that aerobic exercise has no overall effect on pain in a mixed population sample, but individual factors such as fitness level and sex might play a role.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
The revised version of the manuscript upfront highlights the null results regarding the effect of exercise in the overall sample before exploring the effect of individual fitness level and sex differences. To do so, the behavioural and neuronal findings of exercise on pain perception were reported and discussed in more detail.
