Friday, August 15, 2014

Science Friday: Chasing the Runner’s High

A few weeks ago, my mom asked about advice for a family member who just started running. “She’s complaining she can’t get that runner’s high yet. It’s still not very fun. How long does it take?”

How long of hating running before you love it? How long, despite the sweat in your eyes and the exhaustion in your legs, until you cherish it? Like a morning cup of coffee, you crave it, you need it. Gimme the good stuff. You become addicted to the runner’s high, that feeling where a run becomes relaxing, calming, cathartic. But it doesn't come with every run, and it doesn't start on your first trek out. What causes the runner's high and how can we get it? 

The runner’s high is classically blamed on exercise-induced release of endorphins, the body’s natural morphine, its natural pain relievers. Recently, another class of molecules, endocannabinoids, has shared some of the credit. Endocannabinoids are the body’s natural THC (the active ingredient in marijuana), its natural calmers.

A brief foray into how the thinking has bopped around a bit: Endorphins were initially held responsible for the runner’s high because they could be detected in the blood after exercise. But endorphins are too large to get from the blood into the brain—where they would need to be to affect mood—so their role was dismissed. Some even took this to mean the runner’s high was a hoax. Researchers desperate to prove the runner’s high was real discovered that endocannabinoids are made in the brain following exercise and lead to a sense of calm. Voilà. Endocannabinoids stole the show. But the endorphin proponents would not be silenced. Advancements in neuroscience allowed them to see that endorphins are actually made in the brain as well. The moral of all this back and forth research: endorphins and endocannabinoids deliver a one-two punch. Less pain, more calm. (Also, the runner’s high is real, and don’t tell a researcher who runs that it’s not.)

Back to the main question: how many pills do you have to pop to get the high?

Most of the endorphin research is focused on endorphins in the blood; the more recent discovery of brain endorphins means there hasn’t been much written on the intensity or duration of exercise needed for their release in the brain. We do know that exercising at over 75% VO2max (75% of maximum aerobic capacity) caused a spike in blood levels of endorphins. For cyclists pedaling at about lactate threshold (roughly equivalent to tempo run effort), endorphins increased after 60 minutes.

After an hour at lactate threshold (when lactate is produced and
cleared at an equal level), beta-endorphin increases in the blood of cyclists.
We might speculate that brain endorphins would follow a similar pattern. The study that found endorphin release in the brain only looked at one time point—after a two hour run. Two hours was long enough for the participants to have both a surge of endorphins and good feelings. Below is a graph of how they felt after doing nothing (rest) and after running. Happiness and euphoria increased significantly. Interestingly, fatigue didn’t change at all. (I told you long runs are energizing! Or at least not as exhausting as you would expect.)

VAMS is a scale for evaluating mood. Following a run, levels of happiness
and euphoria were significantly increased compared to rest. 

(Mostly unrelated—but too hard to resist—aside: if you feel so inclined to go for a little bike ride during labor, the ensuing endorphin release can help with the pain of delivery. Let me know how that works out for you.)

Endocannabinoids are released in a similar way. In one study, endocannabinoid levels increased after an hour of running or cycling at a moderate pace. In another study, researchers looked at thirty-minute runs of varying intensities. After a slow jog or a medium intensity run, endocannabinoid levels skyrocketed. However, after a high intensity workout (or an easy walk), there was no endocannabinoid increase. In the paper, the researchers say, “High intensities lead to limited changes in mood or affective state.” I’m not sure I entirely agree with this. Maybe because I have been a running addict for years I have built up quite a tolerance, but I think the really tough workouts can be some of the most psychologically releasing. After they end, of course. 

Luckily, both these molecules get released under the same conditions: moderately intense exercise, a solid tempo or a long run. These also happen to be the workouts that might require an extra push to get through. Our brain senses that and kicks on to give us the good stuff when we need it.

As for beginners, the news is less heartening. It takes a while before you can start grinding out these intense workouts or logging hour-plus runs. Fortunately, other benefits of running (strength, energy, weight-loss, health) may be more immediate. Take comfort that with each run you’re many steps closer.

This week, our family’s newest runner finished her first 5k. I’d say she’s well on her way.

Dream big and keep getting your fix,