"People used to think that being skinny was beautiful, especially for women," she said. "But now the concept has been changing, with more and more people appreciating the beauty of a healthy, slim, or even muscular shape."

Meanwhile, customers are paying more attention to the quality of classes, another change brought by the increased awareness of fitness.

Liang Junyao, a 30-year-old graphic designer who takes classes at Supermonkey, said small-sized ones can greatly improve her athletic ability, since coaches can take care of each member and offer advice.

Liang said a traditional gym may be more suitable for those who have already formed fitness habits, have a certain level of knowledge of the subject, and know how to use the facilities, while small-sized classes are ideal for newcomers or those who need inspiration and instruction.

"Many traditional gyms have similar courses, but they always have too many members at a time when the coaches may not have proper qualifications," he said.

Liang has frequently attended a group class studio at Supermonkey, whose instructors all have international qualifications, and some are even regional project leaders for world-class fitness regimens in China.

Li, from Keep, said most of the coaches at Keepland are self-trained, but he will invite some from the industry with the right qualifications to work part-time, especially when there are not enough coaches to match the number of courses.

Keepland recently signed an agreement with the Champion Foundation, which was established by former speed skater Yang Yang in 2008 to help retired athletes. These athletes have provided a steady supply of coaches for the brand.

Keep is also preparing to launch a virtual coaching service by using artificial intelligence.

By combining all the exercise data from online users, as well as smart health and fitness facilities, Keep believes virtual coaching services can help more consumers to access personalized coaching services relatively cheaply.

With consumption upgrades accelerating, more people are paying attention to their quality of life and physical health, and are more willing to pay for "fitness consumption", according to a report on Chinese consumers released by consulting company Accenture in July.

Last year, the value of China's fitness industry was about 150 billion yuan ($21.43 billion), and its compound annual growth rate in the past six years was 7.7 percent, according to analysis company Zhi Yan.

Targeting clients ages 25 to 35 in first- and second-tier cities, Supermonkey wants to take the retail route to encourage more people to work out, Xia said, with the main consumption method being pay-per-visit.

Each class costs less than 100 yuan at most of the facilities, including Keepland, Supermonkey and Space-Cycle. In addition to paying each time they visit, customers can choose to buy packages for fitness classes.