Researchers showed that plasma levels of anandamide-related mediators such as palmitoylethanolamide and oleoylethanolamide were increased after heavy aerobic exercise.
The authors concluded:
these results suggest that the endocannabinoid system mediates aerobic exercise-induced antinociception at peripheral and central levels.
Source: Souza GG, Romero TR, Silva JF, Aguiar DC, de Paula AM, Cruz JS, Parrella C, Piscitelli F, Duarte ID, Di Marzo V, Perez AC The endocannabinoid system mediates aerobic exercise-induced antinociception in rats.Neuropharmacology. 2013 Oct 19. doi:pii: S0028-3908(13)00429-2. 10.1016/j.neuropharm.2013.09.022.