Do endorphins really bond friends together?

The idea is Robin Dunbar's, and it is plausible but only partly tested. Manninen and colleagues (2017, Journal of Neuroscience) used PET scans on 12 healthy men and found opioid release in the thalamus, caudate nucleus and anterior insula after 30 minutes of laughing at comedy with friends, compared with 30 minutes alone. That shows opioids respond to social laughter. It does not show that the release is what makes the friendship last, and the sample was small and all male.

What is pain threshold, and why do these studies use it?

It is the point where pressure or cold first registers as painful, often measured with a blood-pressure cuff inflated on the arm. Endorphins are hard to measure in a living brain without a scanner, so researchers treat a rise in pain threshold as an indirect sign of opioid release. In the 2010 rowers study the cuff reading rose about 11 mmHg after crew rowing and about 5.6 mmHg after rowing alone. It is a proxy, and other things that change with exercise can move it too.

Does the activity have to be in perfect sync to work?

The evidence varies by activity. The rowers matched strokes, and Tarr, Launay and Dunbar's silent disco study (2016) varied how well dancers matched moves. Wiltermuth and Heath (2009) found that groups of three who walked in step cooperated more in later games than groups who walked normally, with no extra positive mood needed. For laughing and eating there is no beat to match, so the shared timing is looser and the evidence is weaker.

How often should friends do something like this?

No study gives a dose for friend groups. The singing and rowing studies measured single sessions or a few months of weekly classes, not decades of friendship. Dunbar's 2017 survey of social eating found people who ate with others more often reported more friends they could count on, but that survey was cross-sectional, so it cannot say frequency causes closeness.

9 Things to Do With Friends, Ranked by the Rowers' Pain-Threshold Evidence

Twelve Oxford rowers raised their pain threshold by about 11 mmHg after rowing as a crew and by about 5.6 mmHg after rowing the same effort alone. That 2010 result from Robin Dunbar’s group is the seed of a whole genre of research on why doing things in time with other people makes them feel like yours.

The short answer for anyone planning a weekend: the activities with the best evidence for bonding are the ones where bodies move or make noise together, such as laughing at the same joke, rowing or training in step, singing, and dancing. Sitting side by side watching something has weaker backing. The evidence is real, small-sample and mostly built on a proxy measure, so treat the ranking below as a way to choose between options, and as a long way from a prescription.

What did the rowers study find, and how small was it?

Cohen, Ejsmond-Frey, Knight and Dunbar published “Rowers’ high: behavioural synchrony is correlated with elevated pain thresholds” in Biology Letters in 2010. Twelve male rowers from the Oxford University Boat Club squad, average age about 24, each did a 45-minute ergometer session alone and another as part of a six-person virtual boat, repeated across two weeks. Power output was matched across conditions. Pain threshold was measured with a blood-pressure cuff before and after.

Rowing alone raised the threshold by 5.63 mmHg on average. Rowing in the group raised it by 11.04. The group-versus-solo difference reached p = 0.038, which is a result that counts but not one that settles the question. One rower was excluded, all participants were elite men from one club, and the authors say the exact feature of group training responsible is unknown. Pain threshold stands in for endorphin release here; no one measured endorphins.

Which nine friend activities have the strongest case?

Ranking criteria: how directly the study measured opioid release or bonding, how close the setting was to something friends could do on a Saturday, and how much the result depends on a handful of participants. The order is my judgment, and reasonable readers could shuffle the middle.

1. Laughing together

Dunbar and colleagues reported in 2012 (Proceedings of the Royal Society B) that across six experiments, pain thresholds were higher after laughter than in control conditions, using laboratory videos and live stage comedy. Press coverage of the paper put the average boost at roughly 10 percent after 15 minutes of comedy in company. Then in 2017, Manninen and colleagues (Journal of Neuroscience) scanned 12 healthy men with PET after 30 minutes of comedy clips with close friends versus 30 minutes alone and saw opioid release in the thalamus, caudate nucleus and anterior insula. It is the only entry here with imaging, and 12 men is still 12 men. Cheapest option on the list: a comedy night where you sit near each other.

2. Rowing, cycling or running in step

The 2010 rowers study above. Nothing says an indoor cycling class works the same way, because nobody tested it, but a group workout where pace is matched is the closest relative. Boats, tandem bikes and a run where you keep the same cadence all qualify.

3. Singing in a group

Pearce, Launay and Dunbar (2015, Royal Society Open Science) followed newly formed adult-education classes over seven months and found singers felt closer to their group faster than crafts and creative-writing classes did, though the others caught up. Weinstein, Launay, Pearce, Dunbar and Stewart (2016, Evolution and Human Behavior) tracked a community choir in small groups of 20 to 80 and a combined group of 232 over 90 minutes of singing and reported raised pain thresholds in both. If you want the story of how karaoke fits, the karaoke ice-breaker write-up covers it; the angle here is what to pick next.

4. Dancing in sync

Tarr, Launay and Dunbar’s “silent disco” study (Evolution and Human Behavior, 2016) manipulated how well dancers’ moves matched and reported higher pain thresholds and more social closeness with synchrony. Participants were strangers to each other, and no one has tested the same setup on established friends.

5. Drumming or playing instruments

Dunbar, Kaskatis, MacDonald and Barra (2012, Evolutionary Psychology) ran four experiments and found that singing, dancing and drumming raised pain tolerance while listening to music and low-energy musical activities did not. Playing badly together counts. Playing a playlist does not.

6. Walking in step

Wiltermuth and Heath (2009, Psychological Science) had groups of three walk around campus in step or normally; the in-step groups cooperated more in later economic games. Two follow-up experiments used cup-moving and singing. This is evidence about cooperation, not endorphins, so it ranks lower on the question asked here. It is also the easiest to try tonight.

7. A long shared meal

Dunbar’s 2017 paper “Breaking bread” used a UK national survey and found people who ate socially more often reported greater happiness, more trust and more friends to rely on. Cross-sectional data cannot prove the meals caused the closeness, and the most bonded meals in his analysis involved more people, laughter and reminiscing, so number 7 leans on number 1.

8. A weekly walk, run or park event

A standing slot such as the one described in the Saturday parkrun friend-date piece is the practical wrapper for several items above. Direct evidence for bonding is thin; the case is that repeated shared movement is cheap to schedule.

9. A synchronized wake-up clip

Untested, and included because it is easy to try. Each friend agrees on the same silly 3-second gesture, records it after getting up, and sends it to the group chat. Nobody has measured whether that produces anything beyond a smile.

How do you turn this into something friends will show up for?

Two practical points from Dunbar’s other work. First, the inner circle holds only around five people, so a ritual like this is built for them; the Dunbar circles piece explains the sizes. Second, closeness takes hours. Jeffrey Hall’s research puts casual friendship at about 50 hours together, friendship at about 90 and close friendship at 200 or more, which the hours-to-friendship breakdown covers, so a single dance night will not do the job alone.

A small, repeatable and slightly ridiculous invitation is easiest to say yes to. Pick one item from the top five, fix a start time, and make the first meeting short enough that no one dreads it.

DontSnooze, the iPhone app that asks for a video within 30 seconds of the alarm or sends a camera-roll photo to your friends, can host item 9 if your group wants it. The point is that your friends see the clip; nothing about the app produces endorphins, and it is one tool among a long list.