A study by Raichlen et al. (2012), “Wired to run: exercise-induced endocannabinoid signaling in humans and cursorial mammals with implications for the ‘runner’s high,’” investigated the phenomenon. The researchers predicted that running would result in chemical reactions in the brain associated with pleasure in species with a history of endurance running, but not in species whose natural history does not include running. They studied three types of mammals—humans, dogs and ferrets—and found that the two with distance running in their evolutionary pasts (humans and dogs) exhibit elevated levels of one particular endocannabinoid (anandamide) after running on a treadmill. Ferrets, noncursorial animals, had no such chemical response.
Both canine and human brains are made to enjoy running, but this pleasurable, rewarding quirk of chemistry is not universal among mammals. Ferrets, as the study showed, derive no pleasure from it. (Friends who despise running have expressed alarm at the results of this study—it makes them wonder if they are part ferret.)
The behavioral benefits to dogs of running may be related more to contentment than to fatigue. Perhaps, what we call “tired” is actually better described as “happy,” “relieved of anxiety and pain” and “experiencing feelings of well-being.” If so, exercise may indirectly benefit dogs’ behavior because it elevates mood rather than simply makes them too worn out to misbehave. Since endocannabinoids lessen the anxiety that can be a source of problem behaviors, it’s easy to see how exercise could help.
Running is also associated with the production of other chemicals that reduce anxiety in mammalian brains. Schoenfeld et al. (2013) reported that mice given the opportunity to run handled stress and anxiety better than sedentary mice. The study observed the brains and brain activity in both groups of mice and found that runners had more excitable neurons in the ventral hippocampus, which plays a role in anxiety, than did sedentary mice. However, the active mice also had more cells capable of producing the calming chemicals that inhibit activity in that area of the brain, which lessens anxiety. The study supports the idea that for mice, at least, running improves regulation of anxiety through inhibitory activity in the brain. It is possible that the situation is similar in dogs, though without studying them specifically, we can’t know for sure.
Of course, behavior and physiology, and the links between the two, are never completely straightforward. There is evidence that cannabinoids can cause hyperactivity at low doses, even though they have calming effects at higher doses. What does this mean for our dogs?
Age, breed and individual differences play a role in the amount of exercise required to keep dogs’ halos on straight and prevent them from sprouting little horns, behaviorally speaking. Some thrive on small amounts of exercise. For others, the same amount of exercise— perhaps a leash walk at a leisurely pace—has the opposite effect. It invigorates them, and may actually induce hyperactivity. (That’s a bit discouraging for those of us whose goal is rarely, if ever, to pep dogs up, though some who compete in canine sports try to do exactly that.)
Recently, I was concerned that I might be inadvertently energizing a dog my family was watching. Super Bee, a Border Collie, belongs to professional runner and Adidas Ultra Team member Emily Harrison. Emily often trains with her dog, so Super Bee typically runs 60 to 70 miles a week. To say she is extremely fit is an understatement along the lines of me saying I sort of like dogs.
While Super Bee was with us, we made exercise a top priority. She went along on all of my morning runs, and my husband ran with her in the evenings. We supplemented this activity with long sessions of fetch; luckily, neither our kids nor Super Bee became bored with this game. Still, knowing that despite our best efforts, we would be unable to give Super Bee her usual amount of exercise, I worried that the shorter sessions would just amp her up.