"We noticed that they would begin to worry about their level of exercising," Spicer said. One employee interviewed by the book's authors said that he felt the need to stay fit to keep his job: "In these times when people are laid off due to the global financial crisis, you need to stay fit, and the health profile helps you do so."

More broadly, Spicer and Cederström found that more extreme corporate wellness programs such as those at Scania lead to increased anxiety and stress.

"In the Scania case, they said: 'I have to exercise or else I’m not going to be seen as an attractive employee. I’m not going to just be a bad person, but an unemployable person,'" said Spicer, who studies organizational behavior, psychology, and sociology of work at the Cass Business School in London.

As health-care costs grow, many companies in the U.S. have invested in some kind of wellness initiative, hoping for a healthier (and therefore cheaper) workforce. A 2013 analysis by the RAND Corporation found that half of all organizations with 50 or more employees offered wellness programs.

The thinking goes that getting at-risk workers to change bad habits will save a company on medical costs down the road. The programs differ, but often include such elements as smoking cessation assistance, biometric screenings, and fitness challenges. According to a Kaiser Family Foundation survey from last fall, 36 percent of large companies offer employees health insurance discounts for weight loss and smoking cessation. Health risk assessments are even more popular, the study found, with more than half of large companies providing a financial incentive for participation.

Despite the growing popularity of wellness programs, it's not clear that they work.

Corporate wellness is an $8 billion industry; as of 2013, employers spent $2 billion on wellness initiatives, as Bloomberg reported in 2013.

While one Harvard study from 2010 found more than $3 in savings for every dollar spent, more recent research by RAND estimated that figure at $1.50.

The same RAND study found much higher savings for disease management programs, as did this study of a successful Pepsi wellness program that, in part, targeted participants with ailments that include asthma, coronary artery disease, atrial fibrillation, and diabetes.

More extensive programs that include preventive measures, however, can actually have unhealthy outcomes, largely by triggering feelings of anxiety, Spicer and Cederström found.

"This increasing pressure ... is not just formal in terms of the wellness programs, but informal in terms of social pressure to work out and be extremely fit in the workplace," Spicer said. "That then can have some psychological effects. There is this implication that you don't just need to have a work ethic, but a workout ethic."

Most companies aren't as overbearing as Scania, but Spicer says that wellness programs have become more aggressive. In some Danish municipalities, for example, employees can participate in sessions with consultants to learn better eating habits. In their book, Spicer and Cederström refer to such programs as "fat therapy." Such initiatives might lead to weight loss, but they publicly single out some workers, and, the two say, imply a lack of self control.

An employer might care less about triggering anxiety than stamping out more concrete risk factors. Still, having anxious employees misses a major aspect of wellness. "Many people have bought into the argument that the fit employee or the happy employee is the most productive employee," he said. "[But] wellness is happiness and health."

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