Michael Rubin has a philosophy about exercise: If it's not fun, he won't do it.

That's why the 50-year-old assistant attorney general won't be taking the stairs to his office — "They're boring." But he can be seen taking a spin at the downtown ice skating rink during his lunch break.

"Somehow, when people start their careers, get a family and settle down, they lose the fun instinct," said Rubin, of Glocester. "But activities like ice skating keep you outside, in the fresh air. That's fun."

Rubin is among a growing number of adults hitting the ice for fitness and pleasure, according to the U.S. Figure Skating Association (search).

Avid skaters say ice skating provides a perfect winter alternative to their normal routines of bicycling, running or in-line skating in the summer.

"The gym gets a little boring," said Bhamati Viswanathan, 41, of Boston. "I like to run in the summer and I needed an outdoor activity for the winter."

Rubin began skating more than 25 years ago, while in college in Pennsylvania. After moving to Boston a few years later for a job, he bought hockey skates, which he found more comfortable for doing laps around the rink.

For the past five years, he has skated an average of about three times a week in the wintertime.

"I was the first person to buy a season's pass here," he said between laps during a recent visit to the Bank of America Skate Center in the heart of Providence's financial district.

"It's really for my psychological health even more than my physical health," he said. "Though I know it's good for that too."

According to Dr. Angela Smith, an orthopedic surgeon at the Sports Medicine and Performance Center at Children's Hospital of Philadelphia, ice skating has less impact on joints than other aerobic activities like running, and it improves balance and increases endurance.

"It's also one of those sports you can do for a lifetime. It does not require a partner or a team, but can be as social as you want it to be," said Smith, an avid skater herself.

The exercise also is good for the waistline. The American College of Sports Medicine (search) says that on average, for every hour of continuous skating, a 150-pound person burns about 600 calories. That's about the same as running five miles in an hour.

The calorie burn increases to about 800 an hour by adding the basic skills of skating, which include forward and backward crossovers, turning, stopping and changing feet.

"Obviously it works the lower body," Smith said. "But you're building bone, raising your heart rate and even working your upper arms and shoulders."

Smith suggested skaters also try to strengthen their backs and abs with core exercises, like Pilates (search), while off the ice. She said in the offseason, cycling most mirrors skating in terms of the muscles used.

"There also tend to be less injuries than with say, in-line skating, which people most closely associate with ice skating," she said.

Adults who want to burn the maximum calories, or just want to gain more confidence on the ice, can join a learn-to-skate program. Many ice rinks — both indoor and out — have added adult programs for those who want instruction in the basic skills without the pressure to compete with fast-learning children.

Coaches say the biggest obstacle for adults wanting to pick up the sport is the fear of falling. A lesson helps adults get over that fear, "and learn to fall correctly," Smith said.

Also, since skaters are continually faced with new challenges, Smith said, individuals incorporating skating into their fitness regime are less likely to get bored and quit.

"You can just flow and you don't have to think about it," said Conor McLaughlin, 24, of Boston, who skates at Frog Pond in the Boston Common three to four times a week.

McLaughlin started skating four years ago, after quitting a high-stress job. He found being on the ice relaxing. Completely self-taught, McLaughlin said he learns new moves by watching figure skaters on TV.

"It's not conformed motion like being at the gym," he said. "It's like dancing on the ice."