PF Episode 30: This is Your Brain on Exercise

Jen: Welcome to Practically Fit, Real Fitness Over 40. I'm Jen Chamberlain.

Alex: And I'm Alex Johnson.

Jen: And today we're going to talk about endorphins, endocannabinoids, and other chemicals your brain produces in response to exercise. Is runner's high real, and how can you get it? We'll talk about all that and more. But before we dive into the science, I wanted to do a little self-congratulation — Alex, this is our 30th episode of Practically Fit. I'd say that's pretty impressive.

Alex: Yeah, I agree. I think our biggest challenge for this episode is actually just going to be pronouncing the word "endocannabinoids" — we're going to be stumbling over that one as we talk through the episode. But it's exciting that we've hit 30 episodes. So thanks to all the listeners, and here's looking forward to another 30 more — we'll see how far we go.

Jen: And thanks to you, Alex, for filling in for two weeks while I was on vacation. I thought both episodes were really interesting and insightful, and I hope our listeners enjoyed them too.

Alex: Yeah, that was fun, but I've got to say, I missed having you on the podcast — so glad to have you back.

Jen: And I'm glad to be back. So let's dive into the science behind these mysterious chemicals that cause this elusive runner's high — something I've actually been thinking about for probably 20 years now.

Alex: Yeah, and just the research we did for this episode really blew my mind. You hear about endorphins all the time, but when you really dig into it, it's fascinating — and it's fascinating that we'll be talking about endocannabinoids.

The Science: What Actually Causes Runner's High?

Jen: Yes, indeed. So whether you call it runner's high or just being "in the zone," I think what most people picture, like you said, Alex, when they think about that good feeling that comes from exercise, is endorphins. But the science around feel-good chemicals has actually shifted quite a bit over the years, so you'll definitely learn something in this one. As it turns out, while the body does produce endorphins — a kind of natural opioid — in response to exercise or stress, endorphins can't actually cross the blood-brain barrier. So they can't be responsible for that blissed-out feeling you sometimes get from exercise. Instead, scientists now think endocannabinoids may be responsible.

Alex: You got it that time.

Jen: All right, I knew I'd get it eventually — I've been working on this. Endocannabinoids. These chemicals work to maintain homeostasis, the balance in your brain and body, and just as the name suggests, they're similar in chemical structure to cannabis.

Alex: So "runner's high" is actually a very appropriate name.

Jen: Yeah, and even funnier, because when it was first named, nobody realized it was from this substance our body produces that's similar to cannabis. And, quick note as we go through this: "endo" means your body produces it, as opposed to some synthetic form of the same chemical.

Alex: Or something you get from a plant.

Jen: Exactly, exactly. So I found a 2021 article in the New York Times that did a great job summarizing several studies pointing to endocannabinoids as the true source of runner's high. It goes back to 2012, with a study of dogs, ferrets, and humans, where researchers had them run on treadmills. I would've loved to see the little ferret treadmill they used for that.

Alex: I'm pretty sure that's the second ferret reference on this podcast in the past few weeks — I think I brought up ferrets while you were gone.

Jen: I think you did too — that's really weird. Well, they're chosen partly because they're not that similar to humans in this respect. Dogs and humans are well adapted to distance running, thanks to some structural traits we have, whereas ferrets aren't — as the article put it, they slink and sprint, but they don't really do marathon running. So when researchers had them all run, the dogs and humans produced elevated endocannabinoid levels, while the ferrets did not, because they don't get that high from running — in fact, they don't really seem to enjoy it.

Alex: So there's no ferret marathon I could enter my future ferret in — not a ferret running competition.

Jen: No, they'd only do well at sprinting. A "Ferret 5K," though — I like that. Good branding for a race.

Alex: Yeah.

Jen: So, going back to the science — a 2015 study with mice took this a step further. Researchers blocked the mice's endorphins and put them through a similar running exercise. Mice actually love to run, so they let them run on little mouse treadmills. When they also blocked the endocannabinoids in a separate group and compared the two, the mice with blocked cannabinoids were still just as anxious and twitchy, as the article put it, as they'd been at the start. But the mice with blocked endorphins were calmer and more relaxed. So when the cannabinoids were allowed to run through their system, that's what gave them that relaxed feeling after their run. Following so far?

Alex: Yeah, I'm just picturing a mouse run now. This is really fascinating research, though.

Jen: Well, then we finally get to humans, and this was the nail in the coffin for endorphins. This debate went on for a long time — I was kind of following it on the sidelines — but there's a 2021 article titled "Exercise-Induced Euphoria and Anxiolysis Do Not Depend on Endogenous Opioids in Humans." I don't know if I'm saying "anxiolysis" right.

Alex: We don't know how to pronounce it, but it means decreased anxiety.

Jen: Exactly — I had to look it up. So basically, decreased anxiety. This study replicated the mouse study in a double-blind, randomized, placebo-controlled experiment. Participants exhibited increased euphoria and decreased anxiety after 45 minutes of running on a treadmill at a moderate intensity. And the important part: this happened even when their opioid receptors — the things that bind to endorphins — were blocked. So this showed conclusively that endorphins couldn't be responsible for the runner's high, and it's now strongly believed that endocannabinoids are the actual cause.

Alex: Cannabinoids, or endocannabinoids?

Jen: Endocannabinoids.

Alex: See, we told you — by the end of this podcast, we'll have edited out the word "endocannabinoids" like 20 times. It's genuinely hard to pronounce. We're trying.

How Much Exercise Do You Actually Need?

Alex: So this is really fascinating. Now that we know endocannabinoids are responsible for the euphoria and decreased anxiety that come from exercise, we were curious exactly how much, and what type of, exercise produces this effect. For that, we turned to research out of Wayne State University by neuroscientist Hillary Marusak. A student in her lab led a systematic review and meta-analysis of 33 published studies on the impact of exercise on endocannabinoid levels. They found that acute exercise — like a 30-minute run or a bike ride — consistently boosted endocannabinoid levels across the studies, and that this boost showed up across different types of exercise, including running, swimming, and weightlifting, and across people with and without pre-existing health conditions. Pretty conclusive stuff. Although only a few of the studies in this meta-analysis looked specifically at intensity and duration, it appears that moderate exercise intensity — like cycling or running — is more effective than lower-intensity exercise, like walking at a slow pace or on a low incline, when it comes to raising endocannabinoid levels. So this suggests it's important to keep your heart rate elevated — roughly 70 to 80% of your age-adjusted maximum heart rate — for at least 30 minutes, to get the full benefit of that endocannabinoid release.

Jen: Oh, good one — you got all the way through that, better than I did on my pronunciation. But the heart rate piece is interesting, because we've looked at this from a lot of different angles, and that was one of the real takeaways for me: you need your heart rate at that 70 to 80%, and 20 to 30 minutes seems to be the sweet spot for getting into that runner's-high zone.

Alex: Yeah, so that lines up. I actually wrote about zone two training last week in our Practically Fit "Quick Hits" newsletter, and zone two was more in the 60 to 70% heart rate range. So this would be more like zone three training — more intense.

Jen: Yeah, absolutely. And the other takeaway is that you don't have to run to get runner's high — so maybe they need a more inclusive term for this feeling. "Exercise high," or something like that.

Alex: Exercise high, yeah — it's not just from running.

Jen: Exactly. Runners tried to own it for years, but I guess we have to give it back. Before we get into our own experiences, though, I wanted to mention another article I came across in Time magazine just a couple weeks ago — fairly recent — highlighting new research showing that exercise can also improve your ability to tolerate pain.

Exercise and Pain Tolerance

Jen: This was an interesting study — it used data from a large Norwegian population of over 10,000 adults, and researchers found that people with more active lifestyles were better able to tolerate pain. They measured this by submerging people's hands in ice water and having them rank their pain on a scale. Sounds fun, right, Alex?

Alex: Yeah, this sounds like just an average day on TikTok.

Jen: It totally does. But the more these people exercised, the better their pain tolerance became — it even improved over the course of the study. Why does this matter? The article notes it's an important finding because, quote, "chronic pain is now more prevalent in the US than either depression or diabetes," and it can be really difficult to treat. We all know a lot of the drugs used to treat it are addictive and come with all kinds of problems. So the fact that exercise can help fight chronic pain is a pretty amazing finding.

Alex: So instead of even smoking marijuana to get your cannabinoids, you could just exercise — that's what you're telling me — and it'll blunt your chronic pain without having to ingest anything. Who knew? Very cool conclusion.

Jen: Yeah, I wanted to circle back to one of the other articles I read, on the mouse studies and so on — it made a very clear point that it's better to get this effect from exercise than from using substances, because exercise doesn't come with the other side effects those chemicals might have.

Alex: Right, it has good effects. No judgment, though, if you want to do it. If you want to eat an entire bag of Fritos this afternoon, go for it — no, I'm just kidding.

Our Own Experiences With Exercise-Induced Bliss

Jen: So I thought we'd close out this episode talking about our own experiences with exercise-induced bliss. Alex, have you ever experienced this, and what kind of activities tend to bring it on for you?

Alex: Yeah, I think the research is spot on, for me at least — I'll be curious to hear your take too. It has to be a bit more intense; I'm not going to get that exercise high from a super slow-paced run, an easy bike ride, or a low-intensity walk. In my experience, it's always been moderate-to-intense exercise that induces the feeling I used to associate with an endorphin rush, and now know is actually my body's own natural marijuana, basically — which, I mean, this research just blew my mind. For me, it's typically been a more intense run or a longer bike ride at a moderate-to-high pace — those are the two things in recent years that have given me that feeling. I've tried to think through other forms of exercise — maybe something like HIIT training could do it too, if we're swinging kettlebells for 20 or 30 minutes, or boxing. But I think it has to be something eliciting more intensity — I don't ever recall getting this feeling from a standard strength workout where I'm taking normal rest periods between sets. But Jen, what about you? What's your experience with this?

Jen: Yeah, absolutely the same, in terms of the types of exercise. But after I've spent all this time throwing endorphins under the bus, I do want to say this next part is purely anecdotal. I've had that relaxed, blissed-out feeling described in the literature after pretty much any intense workout — an hour-long run, even a 45-minute run, a 50-minute boxing session, anything in that elevated-effort range for a sustained duration. But I've also had an interesting experience with really long-distance running, specifically when I was training for marathons. For me, anything over about 16, 18, 20 miles, running gets genuinely painful — your body starts feeling a lot of aches and pains around, I don't know, the three-and-a-half-hour mark. And I've had this experience where I feel that pain, then run past it, and feel this other kind of high that almost feels like a natural opioid — like the pain suddenly just goes away, and it's almost an out-of-body experience. It's very strange. It makes me wonder if there's more to this — I think more research could be done here — but I've definitely experienced different types of so-called runner's high.

Alex: Yeah, I've never experienced that. Honestly, I start to feel the pain around mile nine — the most I've ever run is a half marathon. So no, I've never had that. That's fascinating. I'm trying to think back if I've ever felt that with anything I've done exercise-wise, and I can't recall a time I've had that kind of pain and then worked through it and felt that way. Really interesting — we'll have to look into that more. I'd guess if you look into ultrarunning and things of that nature, that's where you'd find those kinds of stories.

Jen: Yeah, definitely. And you see it too — I volunteered at the finish line of a marathon once, and just watching people cross, with tears streaming down their faces, all these extremely emotional responses — it's fascinating. I'd love to see more research on that.

Takeaways

Alex: Yeah, absolutely. So that was super interesting research — we've learned a lot today. We learned that it's not endorphins responsible for this so-called runner's high that we've all felt after running or other forms of exercise over the years — it's endocannabinoids, which are very similar to what you'd find in marijuana, CBD, and all these shops popping up across the country now. It's all the same underlying concept. This was honestly mind-blowing research to me — I read through it and thought, wow, I learned something new today. Hopefully folks listening feel the same way. And I think the other thing we learned is that it really takes moderate-to-higher levels of exercise intensity to induce that exercise high.

Jen: Absolutely. And we'd love to hear your stories of runner's high, exercise high, whatever you want to call it — I'm fascinated by this subject too, and would love to hear other people's thoughts on it in the comments, or by reaching out to us via email.

Alex: Yeah, bottom line: next time you want to get high, go for a run. There you go. Well, Jen, great episode today. As always, head on over to practically.fit — and if you enjoy the podcast, please feel free to leave us a review on iTunes. We're really excited to be up to 30 episodes, and we're seeing downloads continue to grow, so we appreciate everyone who's been listening. But until next time, remember: fitness is for everybody.