DALLAS — In the months after Doug Robinson started driving a truck, he noticed his clothes were increasingly more snug-fitting. He was already overweight but soon realized that spending up to 11 hours behind the wheel, frequently eating fast food and not exercising was a poor combination.

When his employer, U.S. Xpress, took part in a weight-loss challenge sponsored by the Truckload Carriers Association, the 321-pound, 6-foot-1-inch Robinson signed up.

So far, he’s about 40 pounds into his goal of dropping 100. His truck’s refrigerator is stocked with chicken, tuna and vegetables. And after his day’s drive, he walks — either on trails near rest stops or just circling his truck.

“I have asthma, so with the extra weight on there, it isn’t good for me,” said Robinson, a 30-year-old from Philadelphia. “When I started losing weight, instantly I was breathing better. I was sleeping better at night.”

From trucking companies embracing wellness and weight-loss programs to gyms being installed at truck stops, momentum has picked up in recent years to help those who make their living driving big rigs get into shape.

“I think a lot of trucking companies are coming around to the idea that their drivers are their assets,” said Boyd Stephenson of the American Trucking Associations, the industry’s largest national trade association. He added that healthier employees help a company’s bottom line.

There’s an additional incentive for truckers to stay in shape — their job might depend on their health.

Every two years, they must pass a physical exam required by U.S. Department of Transportation’s Federal Motor Carrier Safety Administration. They’re checked for conditions that might cause them to become incapacitated — suddenly or gradually — while driving, including severe heart conditions, high blood pressure and respiratory disorders.

While there are no weight restrictions, a commercial driver who has been diagnosed with obstructive sleep apnea and isn’t undergoing treatment will not get a medical certificate. Sleep apnea, more common among those who are overweight, leads to daytime sleepiness, a danger on long drives.

But there are obstacles for truck drivers who are mindful of their health. In addition to being seated for many hours at a time, eating options are usually limited to places with parking lots big enough to accommodate their tractor-trailers — most often truck stops, which historically have not been known for wholesome food or workout equipment.

That’s something truck stop chains have been trying to change.

TravelCenters of America, which operates under the TA and Petro Stopping Centers brands, launched a program two years ago called StayFit that includes placing small, free gyms in truck stops, offering healthier eating options and half portions, mapping walking routes near truck stops and building basketball courts in some locations.

“We wanted to remove as many barriers to drivers’ health as possible,” said TravelCenters spokesman Tom Liutkus, who said the company has gyms at 42 of its more than 240 locations, with plans to outfit them all by the end of next year. He added that the gyms have had more than 30,000 users.

Bruce Moss, vice president of human relations for Con-way Freight, said they’ve found that their wellness program reduces the number of people who call in sick, lowers workplace injuries and controls health care costs. The program gives truckers access to wellness coaches and has them stretch before starting a shift.