Ceteris and the optimal exercise regimen

See Let’s Stop Getting Distracted From This Crucial Question About Exercise by Emily Oster, professor of economics at Brown University. 

Ceteris paribus is a Latin phrase meaning "everything else stays the same" or "holding all other factors constant." Oster does a good job of showing that some of the conclusions of exercise research might not be right because of other factors that were not taken into account  

Excerpts:

"Is walking better than tennis? Is running better than swimming? Is it really important to do 80 percent of your workout at 60-70 percent of your max heart rate (known as Zone 2)? These questions serve an engaged population and promise that with a bit more knowledge, you can maximize your health. The trouble is, they are basically impossible to answer well, and most of the answers we get are misleading and wrong."

"The best way to discover the optimal exercise regimen would be with large randomized trials."

"you’d need enormous sample sizes to detect the — most likely small — differences in a statistically meaningful way. Big trials are expensive. And not everyone wants to stick to a randomly assigned exercise program."

"most of the evidence on the so-called best exercise comes from what are known as observational studies."

[they] "ask people about the exercise they already do and compare their health outcomes to those of people who do more or less exercise, or who do different types of exercise."

"such studies almost always confuse correlation and causation."

[one study] "found that swimming didn’t lower mortality, but running did. Does that mean swimming isn’t effective? No. When you look more closely at the data in the appendix of the study, it’s clear what is going on — swimmers were much less likely than runners to engage in other positive health behaviors."

"only about 5 percent of frequent runners in the study smoked, but among frequent swimmers it’s 11 percent — just shy of the U.S. average. Swimmers were also more likely to have high blood pressure at base line, weigh more and have a family history of cancer. One explanation is that doctors may recommend swimming as a low-impact activity for people who already have higher health risks."

"A 2019 study argued that the benefits of walking leveled off at 7,500 steps a day, suggesting that this was a threshold number. But when you look at the paper, it’s clear that the people who walk more are also more likely to do other healthy behaviors (like abstaining from smoking and eating well). A 2025 paper used wearable devices to suggest that one minute of vigorous activity is equivalent to an hour of light activity. But it doesn’t sufficiently take into account that the mere ability to engage in vigorous activity is most likely already a sign of better health" 

Related posts:

A case of ceteris paribus: does moderate drinking harm your health? (2025) 

Great Moments In Causation Vs. Correlation: Eat more chocolate, win more Nobels? (2012)

Banning Cell Phones While Driving And A Lesson In Ceteris Paribus (2010) 

Tough Professors Are Better For Students In The Long Run (2011)

Will Studying Economics Make You Rich? A Regression Discontinuity Analysis of the Returns to College Major (2023)

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