I’ve bored all my friends with this news, so now I’m starting on you lot ― I’ve started taking spin classes twice a week. They’re so intense, they led me to write an entire article about how much pain is too much pain during a workout.

I always leave bright pink, my hair heavy and slicked to my forehead. Yet when my instructor was sick this week, I decided to direct my own solo cycling class ― and barely broke a sweat.

If you also think you go harder in group fitness classes than you do on your own. you’re not alone. After frantically looking up why my biketop behaviour changed so much, I discovered I’ve definitely been hit by the Köhler effect.

Encyclopedia Britannica’s site explains the phenomenon as one which “occurs when a person works harder as a member of a group than when working alone.”

It was first discovered by psychologist Otto Köhler in 1920s Germany.

He got members of a rowing team to curl a challenging 44 kg weight standing up until they were too tired to keep going. They did this alone or in groups of two or three.

The weights doubled or tripled according to how many people were in the teams (so it’d be twice as heavy for teams of two, and thrice as weighty in groups of three).

If participants were part of a group, their whole team would have to stop as soon as one member gave up (this is called a conjunctive group task; if one fails, they all fail).

Teams typically lasted longer than their “weakest” member could manage on their own, suggesting that the stakes of the group dynamic motivated lower-performing members to go harder than they would otherwise.

That difference was greatest when there were moderate differences between the “top” and “bottom” performers.

If one person was miles ahead of the rest, lighter lifters didn’t perform much better than usual; if they were all roughly in the same boat, team members didn’t seem motivated to improve much.

In other words, that girl in my spin class who can hold a sprint for ten seconds longer than me might be pushing me harder than the one who can do that backwards with no hands on the handlebars.

But equally, I’d probably leave my class with a dry brow if everyone around me was puffing along at roughly my own pace.

Yes. Iowa State University says that working out with a friend can increase accountability, help you to form better habits, and even fulfil social needs.

And in case you think Köhler’s advice may have staled since its century-old discovery, take heart: a recent study tested his theory and found that participants who performed a plank next to a more capable partner lasted about 24% longer than they did on their own.