Habits in Physical Activity: Papers We’re Reading, Week 10

July 6, 2021  |  By: Asaf Mazar

Working out is one of the best steps we could take for our mind and body. Regular exercise can dramatically improve heart health, help retain cognitive functioning into old age, and even alleviate depression. And yet, many of us don’t work out as much as we’d like (or should). The Covid-19 pandemic didn’t help either—2 out of 5 U.S. adults reported gaining about 15 pounds between March 2020 and 2021. 

This week’s papers look at the role of habits in physical activity: How long does it take for an exercise habit to form? How do strong exercise habits come into play on those off-days? And is putting on your gym shoes the real habit you should focus on?

Habits to the Rescue When You Don’t Really Feel like Working Out

Working out for a week or two is within most people’s reach (there’s a reason why gyms are packed with the “new year’s resolution” crowd every January). But keeping up the habit over time is a challenge—especially because our intentions are notoriously dynamic. While going for a run can sound good on Monday, by the time Tuesday morning comes around, staying in your warm bed might suddenly sound a lot more attractive.

One solution to this problem is supplementing intentions with a healthy dose of habit. A habit is an automatic association that ties together a context (like waking up in the morning) and a behavior (like going out for a run).  A strong exercise habit can help shield behavior from the ebb and flow of intentions by automatically triggering a behavior at a given context. Think putting on a seat belt (behavior) when you go into a car (context): You don’t need to deliberate and think over whether you really want to buckle up or not—the behavior is activated automatically, probably while you’re thinking of something else entirely. 

This study tracked how habit, intentions, and physical activity interact in real life. Researchers measured participants’ exercise habit strength, then tracked their physical activity using an accelerometer for two weeks. Each day, participants also reported their intentions to work out. The results showed that habits were especially important on days when intentions to exercise were weak. On days when participants had strong intentions to work out, habit strength didn’t predict activity: On those days, weak habit participants were about as active as strong habit participants. But habits came into play on weak-intention days: On those days, strong habit participants were more active than weak habit ones.

Working out consistently is complicated. And unstable intentions make it so that motivation and willpower alone might not cut it. But strong habits can protect behavior from short-term changes in intentions, allowing us to persist over time.

Rebar, A. L., Elavsky, S., Maher, J. P., Doerksen, S. E., & Conroy, D. E. (2014). Habits Predict Physical Activity on Days When Intentions Are Weak. Journal of Sport & Exercise Psychology, 36(2), 157–165.

How Long Does It Take To Make Exercise a Habit?

You’ve probably heard about the 21-day rule: Repeat an action 21 days in a row, and it becomes a habit. Appealing as this rule of thumb is, the reality is not so simple. The 21-day rule originated in a popular 1960’s self-help book by a plastic surgeon named Maxwell Maltz. Maltz noted that in his experience, it took people at least 21 days after plastic surgery to get used to their new features. Decades later, a game of telephone transformed this observation into a supposed rule of habit.

So how long does it actually take for an exercise habit to form? This is the question that the present study tried to answer. The researchers followed new gym members over the course of 3 months and measured their physical activity and habit strength at baseline, as well as weeks 6, 9, and 12. They found that habits mostly formed by week 6, not increasing much afterwards. Further, their data suggested that reaching habit formation required working out at least 4 times per week during this 6-week period.

Most people needed more than just 21 days to form an exercise habit. Even then, there is no magic formula: Another paper studying a range of health behaviors found a median time to habit formation closer to 9 weeks. Still, another analysis using attendance data collected from more than 10,000 gym members found it required a median time of 7 months to build a habit! Habit formation differs based on the target behavior, the person, and their environment. Continued research will give us a better understanding of how, when and for whom habits are formed—but for now, we can embrace that the longer we do something (ideally, for more than 21 days!), the better it will stick.

Kaushal, N., & Rhodes, R. E. (2015). Exercise habit formation in new gym members: A longitudinal study. Journal of Behavioral Medicine, 38(4), 652–663. http://dx.doi.org.libproxy1.usc.edu/10.1007/s10865-015-9640-7

Lally, P. et al. (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology, 40, 998–1009. https://citeseerx.ist.psu.edu/viewdoc/download?doi=

Buyalskaya, A. (2021). ‘Investigating Drivers of Repeated Behaviors in Field Data.’ PhD Thesis, CalTech, Pasadena, California. https://thesis.library.caltech.edu/14116/1/ABuyalskaya_Thesis_Final_5%2027%2021.pdf

The Real Habit Might Just Be Putting on Your Shoes

Some habits come from relatively simple actions: locking the door when you leave the house, or turning on the light when you enter a room. Exercise, on the other hand, is usually a complex behavior. Exercise can consist of a whole sequence of actions: 

  1. Finding time to exercise
  2. Selecting and putting on workout clothes
  3. Grabbing a gym bag
  4. Putting together a second set of clean clothes
  5. Packing these cloths in the gym bag 
  6. Putting on shoes
  7. Commuting to a gym

And all this before even starting your workout!

These initial actions—everything you do to prepare for exercise—are called instigation habits. And these could be different from the actual habit of going through the different steps of your exercise routine, or execution habits. For example, you might prepare for exercise every day in exactly the same way, but then complete a different workout each time. 

Which habit is more important—preparing to exercise, or exercising? The answer to this question is critical because it can guide the amount of variety we aim for in our physical activity. If the key habit to focus is going through the steps of an exercise routine, then you might aim to repeat the exact same routine as much as possible. But if instead the key habit is  preparing to exercise, then choosing different workout routines could be fine as long as the preparation component is habitual. 

Researchers in this present study examined the association between instigation habits, execution habits, and physical activity. They measured participants’ habit strength before and after one month, and had participants report on their physical activity every evening. Both instigation and execution habits predicted exercise, but strong instigation habits were better predictors of daily physical activity than strong execution habits.  

Although we usually think of “exercise” as a single behavior, it is almost always a complex sequence of multiple behaviors. And starting the sequence habitually may be more important than habitually going through its later stages. 

Phillips, L. A., & Gardner, B. (2016). Habitual exercise instigation (vs. Execution) predicts healthy adults’ exercise frequency. Health Psychology, 35(1), 69–77. http://dx.doi.org.libproxy2.usc.edu/10.1037/hea0000249


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