Exercise has solid benefits for mental health. This is well-substantiated in the scientific literature. Higher intensity seems to improve my mood more effectively than slower steady-state exercise. A good body pump following a workout leaves me feeling completely high. This morning, I dragged myself out for a six miler. I’m in a Covid funk. A positive COVID case in my office suite and the ongoing litany of complaints from COVID and vaccine deniers has sapped what I call “life morale.” This is the wrong place for me. Low life morale makes me lethargic and passive. Motivating myself to run or lift becomes difficult. If I succumb and start missing workouts, I will rapidly spiral downward.

With this in mind, I began my run. As I clicked off the miles, my thoughts focused on telling myself that this is where fitness gets done. Not every run can be a singular occasion to bond with body and nature. Sometimes, it is just about getting out there and trudging through the miles. Usually, by about mile three, my spirits have lifted. I ease into the rhythm of the run, and my pace quickens by over a minute per mile. I must consciously dial down my enthusiasm and force myself to slow down. Not today. Mile five was no more lively than the first.

I recently read “Run Less Run Faster,” which advances a running program based on running quality miles only, based on Jack Daniels’ VDOT calculations. Since it was after dawn, I decided to add the first repeat workout for 5K training: 2 x 400 meters. The two repeats were unexpectedly easy at my prescribed pace. I started at a minute per mile faster and had to slow down to get within range of my pace. More importantly, the quicker running seemed to peel back my funk. After just a couple of minutes of feeling my heart rate go up, of feeling my body begin to burn oxygen at a near-anaerobic pace, running at 85-90% of my maximum effort, my fog cleared away.

We now know that the runner’s high is often produced not by endorphins but by endocannabinoids, typically after several hours of vigorous activity. Short repeats stimulate dopamine production, the pleasure response system at the heart of all addictive behaviors and drugs, from cannabis to alcohol to oxycontin. Dopamine is evolution’s reward system for behaviors that increase the reproductive success of hunter-gatherers, long-distance hunting and gathering, eating high-calorie foods, and sex. Today we no longer persistence hunt, but regular exercisers enjoy the rewards of the long hunt. Regular exercise increases the sensitivity of dopamine receptors and stimulates the neurotransmitter’s production. Athletes get a dual reward: more dopamine and greater sensitivity to it. When I downshifted and sped up for those repeats in the last mile, I gave myself an unanticipated dose of dopamine. I expected that the faster running would increase my discomfort.

Instead, it made me high, and the high has lasted all day.