During a recent Zumba class, an emaciated woman came in late and began to follow the movements.
One participant was alarmed enough to tell the front desk. "I was very concerned she would break a bone or have a heart attack," said the woman, who did not wish to be identified. "It seems that for a sports club to let somebody like her exercise is similar to a bar serving drinks to a very drunk customer."
It turns out that a fitness club's legal authority when it comes to dealing with people with an eating disorder, such as anorexia or bulimia, is a pretty grey area.
In a 2011 briefing paper, the International Health, Racquet & Sportsclub Association, which serves the global health club and fitness industry, stressed the importance of fitness clubs educating themselves to recognise the signs of eating disorders.
The paper said clubs "do not have a specific obligation" to inform members about anorexia and bulimia but should do so to protect the club and its employees from liability and to protect a member's health.
Clubs should include eating disorders in disclaimers and medical clearance forms and treat them like any other medical condition, said the association.
Ms Claire Mysko, chief executive of the National Eating Disorders Association, said fitness centres, trainers and coaches are on the front line in helping people with eating disorders.
"They are in a position to recognise behaviours and if they are witnessing dramatic weight loss in a person, they can intervene to try and help," she said.
However, she added that it is hard to tell if someone has an eating disorder just by looking at him. "Anorexia is the most visible disorder when a person is severely underweight, but people with eating disorders can be of normal weight or overweight," she said.
The issue of how the fitness industry deals with members with eating disorders is psychotherapist Jodi Rubin's mission.
Ms Rubin, who specialises in eating disorders, would go to her gym and see people spending hours working out. "Overexercising is often a sign that someone has an eating disorder and I'd see fitness-club employees not knowing how to handle such a situation," she said.
"This is not about asking someone who visibly has an eating disorder to leave the gym. It's about understanding the dangers and destructiveness of the disorder and offering your help."
Ms Rubin became certified as a fitness trainer so that she could provide online training courses to coaches through her Destructively Fit website. Her courses highlight how to spot the signs of overexercising.
She said: "If you never take a day off from exercising, feel depressed or anxious if you miss a day at the gym, or give up social engagements to exercise, those are signs of overexercising."
Gym member Lauryn Lax said if fellow members of the YMCA club in Nashville had not approached her in 2014, she might be dead today.
She had struggled since she was 10 with an eating disorder. She weighed 35kg in 2014 and was working out up to eight hours a day.
She said: "The gym members said they were worried about me and wanted to take me to hospital."
Ms Lax went to hospital and started her long road to recovery. She is now a doctor of occupational therapy and a nutritional therapy practitioner in Texas.
She said the only time she was approached out of concern for her health at a gym was at the YMCA club.
"Coaches at other clubs would talk to me in a way that did not address my problem outright," she said. "Some would say 'Oh, back again?' in a backhanded way. That's why I had several gym memberships."
Ms Lax added: "That accelerated my eating disorder even more because I wanted to cling to the exercise regimen even more."
THE WASHINGTON POST