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Gym members are “the fruit fly of habit research”, in the words of behavioural scientist Katy Milkman.

Natural scientists keep coming back to experiment on the flies, because the insects share 60 per cent of their DNA with humans. Similarly, social scientists swarm around gym users, or at least their data, to work out why people stick with, or drop, healthy workout habits.

Milkman is both a gym-goer and, as a professor at the Wharton School of the University of Pennsylvania, an avid student of other people’s gym-going habits. Her interest goes well beyond the locker room, though. Find the key to good repeat behaviour, she suggests, and you can use it to unlock motivation at work or in your studies, or build a better and more productive business.

At this point in 2022, you may have started worrying about that new year resolution to visit the gym more often. Don’t panic. Milkman demonstrated in previous research that there was no particular reason why you had to wait for January 1 to come round again to pledge to change your behaviour. Identifying what she called “the fresh start effect”, she found that pegging a life change — be that increased savings, a change of job or a new fitness programme — to any significant date, such as a birthday, increased the effectiveness of the pledge.

In separate work, she also looked at the difference between “Routine Rachels”, who set rigid times for gym visits, and “Flexible Fernandos”, who were permitted to adjust their timetable. After running a study with Google employees, she found that allowing flexibility encouraged more lasting gym attendance. “The most versatile and robust habits are formed when we train ourselves to make the best decision, no matter the circumstances,” Milkman writes in her recent book How to Change.

Milkman’s latest work is on a significantly greater scale. She and Angela Duckworth, best known for her work on “grit” and the book of the same name, organised a “megastudy” in partnership with the 24 Hour Fitness chain, simultaneously testing on its 60,000 members, 54 four-week micro-interventions suggested by dozens of scientists.

Of the ideas they tested, 45 per cent increased weekly gym visits by between 9 and 27 per cent, according to the study, recently published in the journal Nature. All the ideas outperformed a placebo control programme.

The most effective nudge turned out to be the offer of a few pennies of reward, in the form of Amazon vouchers, for users who returned to the gym after missing a session. The study also tested “temptation bundling”, based on ideas Milkman explored in previous research looking at how people are encouraged to go to the gym if they combine visits with the opportunity to listen to favourite audiobooks. Persuasion expert Robert Cialdini, bestselling author of Influence, proposed an experiment that successfully demonstrated the power of simply informing users that most Americans were exercising and numbers were growing. The technique boosted gym visits by 24 per cent.

Physical health is no trivial matter, so if offering tiny rewards can achieve a widespread increase in gym attendance, so much the better. But Milkman believes the structure of this megastudy and others like it is as important as the substance, if not more so.

Through the Behavior Change for Good Initiative, Milkman and Duckworth believe scientists can accelerate their behavioural studies and make them more effective. Scientists submit ideas to participate in what is in essence a massive cross-disciplinary collaboration. The centre sifts and refines the proposals for feasibility, legality and good taste, and then runs the experiments simultaneously, publishing both successful and unsuccessful outcomes.

“The nice thing is that we put it all out there — we hang all our dirty washing and we get to publish the null results alongside the others,” says Milkman. She points out that the exercise is like an instant meta-analysis, or study of studies.

The willing participation of Milkman and Duckworth’s gym-going “fruit flies” is only a start. Megastudies are planned or under way to look at how teachers can improve the performance of their pupils, universities can retain students, people can create emergency savings pots, societies can reduce misinformation and — critically during Covid-19 — patients can be encouraged to consider vaccination.

One 2021 megastudy of 19 ways in which text messages can be used to nudge patients into adopting the flu vaccine offers some hints about what such research might yield. It suggested that text messages sent in advance could boost vaccination rates by an average of 5 per cent. The best results were found after patients were texted twice and told that their flu shot was specifically reserved for them.

In How to Change, Milkman poses this question: “If you can’t persuade people to alter their behaviour by telling them that change is simple, cheap and good for them, what magical ingredient will do the trick?” Megastudies could open a fast track to find the magic spell.

Andrew Hill is the FT’s management editor

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