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Both Sickness and Health, It Turns Out, Are Contagious

I can't wait to join the latest fad! Maybe I'll buy one of those exercise mirrors! Also, I going to start hanging out with people who look like they're carved out of granite.

I'm evaluating getting the Tonal Mirror or the upgrade that Neo uses?

Both Sickness and Health, It Turns Out, Are Contagious

Just like viruses, health fads such as Peloton, Pilates and Zumba spread rapidly and then fade

Peloton’s sales boomed as the pandemic surged, but the exercise-bicycle company posted a $1.2 billion loss for its latest quarter.

Josh Zumbrun, WSJ

Sept. 9, 2022 5:30 am ET

Behind the 95% crash of Peloton’s stock there are two types of contagion.

The first, better-known type is of a highly infectious coronavirus spreading around the world, forcing us to stay home and sparking a massive, ultimately unsustainable boom in sales of the Internet-connected home exercise bicycles. The lesser known type that Peloton typifies is of a highly contagious fitness fad jumping from household to household before running out of newly susceptible households to “infect.”

The analogies between Covid-19 and Peloton aren’t glib. A growing body of research in recent years has suggested that many health behaviors—from obesity to exercise and weight loss, from smoking to quitting smoking—are fundamentally contagious phenomena. The findings, which haven’t gone uncontested, suggest exposure to norms and ideas through your social network could be a powerful predictor of your health, your weight and even the stock prices of companies linked to those things.

“Research suggests that contagion is certainly at play,” said Tricia Leahey, a University of Connecticut professor and co-director of the UConn Weight Management Research Group, who has run a number of experiments over years on the social transmission of weight management. Simply put, “seeing people engaging in a variety of other diets and activities—folks tend to pick it up and try it themselves,” Dr. Leahey said.

It was an unintentional quirk in a long-running medical study that first gave researchers the numbers that showed how health behavior spread through social networks.

Starting in 1948 researchers persuaded 5,209 residents of Framingham, Massachusetts—about two-thirds of the town—to undertake a battery of physicals, lab samples and questionnaires every two years to track their heart health. Over the years, the Framingham Heart Study began to follow children and grandchildren of the original participants.

For decades, administrators kept handwritten notes on close friends and family of participants for follow-up interviews. Because so many residents of Framingham participated, many of the friends and families identified in these records were also participants in the study.

Researchers Nicholas Christakis, then at Harvard, and James Fowler, of the University of California San Diego, went through these records and found 12,067 people who were socially connected at some point from 1971 to 2003. Here was a large social network with carefully collected data points beginning 13 years before Facebook founder Mark Zuckerberg was even born.

Among their landmark findings was that obesity is essentially contagious. Having close friends become obese appeared to increase one’s own risk of obesity. Though there was skepticism about the strength of these initial findings, researchers have moved far beyond the Framingham study in their understanding of contagion.

Researchers have found many new ways to measure social influences, said Dr. Christakis. The use of large-scale randomized trials has helped more clearly establish that social contagion drives health.

Dr. Leahey of UConn has also used randomized trials to show the phenomenon genuinely reflected causation, not correlation, among acquaintances sharing certain behaviors—and not just harmful ones. “We wondered, can the flip side be true? Are positive health behaviors also influenced by social networks and norms?” she said.

One such experiment assigned people to different weight-loss programs with or without extra social components. The social contagion effects were fairly strong: being randomly assigned to socially influential teammates increased the odds of achieving significant weight loss by 20%.

Contagious health behaviors don’t yield numbers such as reproduction rates or herd-immunity thresholds the way viruses do. But researchers have found many ways to quantify these contagious effects. One study found, for example, that spouses who undergo no treatment still lose about half as much weight as a partner going through treatment.

In an annual survey of fitness trends since 2007, Walt Thompson, former president of the American College of Sports Medicine, has documented trends that have come and gone like waves. There was Pilates, hugely popular from 2008 to 2010 before rapidly fading. Boot camps surged in popularity in 2011 then tapered off. Zumba had a moment in the spotlight in 2012 and 2013. Then high-intensity interval training—exemplified by CrossFit—exploded onto the scene.

“You’re always going to get arguments, ‘It’s a trend, not a fad,’ ” Mr. Thompson said. “I think we’ve proven some of them are fads.”

The exercises with staying power, for example yoga, tend to generate new variants, Mr. Thompson said. One variant of yoga, for example, is sweat-drenched hot yoga. Another is yoga nidra, where the goal is to nearly fall asleep. There’s also deeply earnest restorative yoga, and then there’s goat yoga.

For many people, the way they exercise, not just the fact they exercise, is a way to signal virtue, said Natalia Mehlman Petrzela, a professor at the New School and author of “Fit Nation: the Gains and Pains of America’s Exercise Obsession,” a forthcoming book that looks at the history of fitness culture in the U.S.

The signal isn’t exactly about just being healthy. What drives the contagious trends, she said, is people who are signaling “my participation in fitness culture shows I’m on the cutting edge of luxury and fashion and fitness.”

“Since the 2008 economic crisis it became much more distasteful to unapologetically show off fancy purchases,” she said. “But if you show you’re doing something healthy that’s a more socially acceptable way to show off that you’re doing something fancy.”

Clearly Peloton isn’t the cool new thing anymore. The company lost $1.2 billion last quarter. But if the contagion analogy holds, it probably won’t go away entirely. After all, it’s still a great workout if you just want to get on the bike, elevate your heart rate and burn some calories. Like Pilates, Zumba and indeed Covid, Peloton will become endemic—present in the population but, with fewer people left to catch the bug, less contagious.

Write to Josh Zumbrun at

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