New York CNN  — 

Planning to hit the gym during rush hour? You’ll have much better luck finding an open elliptical machine than a bench press, squat rack or 30-pound dumbbells.

Strength training — also called weight training or resistance training — has surged in popularity, driven by new research on its health benefits, the growth of high-intensity gyms like CrossFit, and more women brushing off stereotypes that body building is for men only. It’s just the latest in a series of radical shifts over decades in how Americans exercise.

The pandemic led more people to take up weight training, gym owners and industry experts say. After gyms reopened in late 2020 and early 2021 from Covid-19 safety restrictions, more people rushed to lift weights and use equipment they didn’t have access to at home.

Post-pandemic, the surge in the popularity of weight training has helped the gym industry recover. The number of gym memberships in the United States increased 3.6% in 2021 from pre-pandemic levels, according to the latest data from IHRSA, a trade association for the fitness industry.

Gyms have added more dumbbell racks and other weights to keep up with demand.

Strength training has been the most popular exercise class booked during the past two years, according to ClassPass, a subscription-based fitness app. In 2022, there was a 94% increase in strength training classes from the year prior.

“Strength training has become so much more widely embraced and accepted for all kinds of outcomes — aesthetic, weight loss, bone health and balance,” said Natalia Mehlman Petrzela, an associate professor of history at the New School and author of “Fit Nation: The Gains and Pains of America’s Exercise Obsession.”

At the same time, stationary cardio equipment like elliptical machines and treadmills have seen a dropoff in usage at gyms.

“There’s [fewer] minutes spent on cardio [compared] to pre-Covid,” Planet Fitness CEO Chris Rondeau said on an earnings call Thursday. Planet Fitness members are doing more weight training and functional exercises like push-ups and squats, he said.

Planet Fitness (PLNT) is reducing the available space in some gyms for cardio and adding more room for functional training and kettlebell workouts. (Planet Fitness (PLNT)’ stock has recovered completely from a Covid-related slide, touching an all-time high last year, while Life Time increased 17%.)

Changes in how people exercise have forced gyms to adapt, with new gym designs featuring more dumbbell and squat racks and open areas for lunges, deadlifts and other weighted exercises.

Planet Fitness and other gyms have seen a dropoff in cardio machine use.

“In the past it was ‘let’s cram as much equipment into these rooms as possible,’” said Daniel Allen, an architect who has designed residential and commercial gyms around the country. “Now it’s ‘how much free space can we add?’”

“There’s always people doing kettlebells,” he said. “We’re basing a lot of our initial layouts on making sure we maintain an open zone for those exercises.”

How America exercised

The growth of weight training is a change from how Americans exercised for much of the last century.

During the early decades of the twentieth century, gyms were considered “sweaty dungeons” and the men who went to lift weights there were seen as “unintelligent or effete,” Petrzela writes in “Fit Nation.”

“People thought I was a charlatan and a nut,” recalled Jack LaLanne, founder of the modern fitness movement, who first opened a club in Oakland, California, in 1938. “The doctors were against me — they said that working out with weights would give people everything from heart attacks to hemorrhoids.”

There was also suspicion of women who exercised and concerns it would impact fertility.

Women typically went to separate “reducing salons” or “slenderizing salons,” often located next to beauty salons, to lose weight, Petrzela said.

An advertisement for one mid-century slenderizing machine told women they could do minimal physical activity to lose weight: “Relax in luxurious comfort…No moving from one machine to another.”

In 1968, Dr. Kenneth Cooper published “Aerobics,” a best-seller that encouraged running, jogging and swimming to improve health and reduce the risk of cardiovascular disease. Cooper’s book set off a cardio revolution and became popularized by Jane Fonda’s VHS workout videos.

A Nautilus bodybuilding gym shown in 1983.

The arrival of Nautilus and Universal strength training equipment in the 1970s and 1980s made weightlifting more attractive to a broader range of people. These machines were approachable and had adjustable weight plates that were easy to use.

Nautilus machines helped to bring strength training into the broader mix of exercises. Clubs with Nautilus in their name and the company’s equipment inside began popping up across the country.

‘Everybody is using dumbbells’

But today, free weights have become the more popular form of strength training. And weight lifting has grown in recent years in part due to new research on the benefits.

The latest federal health guidelines recommend at least two sessions a week of muscle-strengthening activities that are moderate- or high-intensity and involve all major muscle groups.

The rise of CrossFit has also led high-intensity workouts with squat racks to become more popular with the broader public, especially among women.

“Prior to CrossFit, that kind of equipment was associated with body building,” Petrzela said. “Seeing a lot of people do that for functional fitness has demystified it.”

Weight lifting has become more popular among women, fitness experts say.

Gale Landers, CEO of Fitness Formula Clubs in Chicago, said his clubs have removed 10% to 15% of cardio equipment to make room for more free weights and benches. Fitness Formula has also added turf areas where people can do functional training.

At Genesis Health Clubs, a chain of 61 gyms mostly in the Midwest, “you’ll go in and see every one of the squat racks full,” said CEO Rodney Steven.

Genesis clubs have added more squat and dumbbell racks to keep up with demand for strength training and downsized cardio areas.

“Free weights are the biggest increase we’ve seen at all our clubs,” Steven said. “Everybody is using dumbbells.”