Planet Fitness is seeing more pre-teens and teens sign up for their first gym memberships during the coronavirus pandemic, helping to fuel the company’s overall growth.

When the gym operator reported its fourth-quarter results on Thursday, it said Generation Z — people born between 1997 and 2012 — was the fastest-growing demographic group for Planet Fitness memberships in 2021.

CEO Chris Rondeau said in an interview that many younger users flocked to its fitness centers last year as school activities and sports leagues were temporarily paused. The trend has continued into 2022, he said, despite the resumption of many group activities and the return of in-person learning at schools.

“This past September, when school sports were in play and recreation centers were back open, [membership rates] didn’t drop off,” he said, adding Gen Zers put extra emphasis on staying active and maintaining their mental health. “They continue to join, quite a bit above pre-Covid levels.”

Planet Fitness memberships start at a monthly rate of $10, which is significantly more affordable than higher-end chains like Life Time Fitness and Equinox.

According to Rondeau, about 62.5% of members have upgraded to Black Card, which is growing in popularity as the company expands. The $22.99-a-month option gives customers access to all of its 2,000-plus gyms in the U.S., along with other perks like tanning beds and guest passes.

At the end of January, Planet Fitness counted 15.6 million members, which it said surpasses its pre-pandemic peak.

Net income attributable to Planet Fitness shareholders for the three-month period ended Dec. 31 fell to $5.7 million, or 7 cents per share, compared with $8.7 million, or 11 cents a share, a year earlier. Excluding one-time items, it earned 26 cents a share, in line with analysts’ estimates for 26 cents, based on Refinitiv data.

Total sales soared 37.3% to $183.6 million from $133.8 million a year earlier. That topped estimates for $178.8 million.

Planet Fitness shares were mostly flat during Thursday trading despite the broader market sell-off. As of Wednesday’s market close, shares were down about 1% year to date.

Find the full financial press release from Planet Fitness here.