Article #31 of 50: I have made it a goal of mine to share at least 50 research articles with you to review in 2012. These articles will be shared with no opinion of mine, just purely the information provided in the research and where to go to read more about the topic. This weekly challenge will feature many different aspects of the field: strength, conditioning, nutrition, psychology, etc. If you would like to submit research articles to be included in this segment, please email me a PDF version of the peer reviewed journal article.
The Journal of Experimental Biology 215, 1331-1336.
Humans report a wide range of neurobiological rewards following moderate and intense aerobic activity, popularly referred to as the ʻrunnerʼs highʼ, which may function to encourage habitual aerobic exercise. Endocannabinoids (eCBs) are endogenous neurotransmitters that appear to play a major role in generating these rewards by activating cannabinoid receptors in brain reward regions during and after exercise. Other species also regularly engage in endurance exercise (cursorial mammals), and as humans share many morphological traits with these taxa, it is possible that exercise-induced eCB signaling motivates habitual high-intensity locomotor behaviors in cursorial mammals. If true, then neurobiological rewards may explain variation in habitual locomotor activity and performance across mammals. We measured circulating eCBs in humans, dogs (a cursorial mammal) and ferrets (a non-cursorial mammal) before and after treadmill exercise to test the hypothesis that neurobiological rewards are linked to high-intensity exercise in cursorial mammals. We show that humans and dogs share significantly increased exercise-induced eCB signaling following high-intensity endurance running. eCB signaling does not significantly increase following low-intensity walking in these taxa, and eCB signaling does not significantly increase in the non-cursorial ferrets following exercise at any intensity. This study provides the first evidence that inter-specific variation in neurotransmitter signaling may explain differences in locomotor behavior among mammals. Thus, a neurobiological reward for endurance exercise may explain why humans and other cursorial mammals habitually engage in aerobic exercise despite the higher associated energy costs and injury risks, and
why non-cursorial mammals avoid such locomotor behaviors.