Washington ? It must be one of the shortest sports seasons going.

People who know they ought to start exercising begin a gym membership at the new year. But after the Super Bowl, their willpower has waned, and they’re gone. Outta there.

Is the timing just coincidence?

Not to James Sallis. The exercise psychologist considers it part of the plot.

“How many commercials, magazine articles and news reports are there about the Super Bowl? Thousands,” Sallis said. “And what are they trying to get people to do? To sit in front of the TV for a minimum of three hours and up to eight hours.”

And while people sit, he said, they “eat what they vowed not to eat and drink what they vowed not to drink.”

To Sallis, it’s not just lack of will that keeps people from following through on their New Year’s resolutions to exercise; it’s because the exercise game is fixed.

“From TVs and movies to cars, huge industries don’t make money when you exercise, and they push things that make you sedentary,” said Sallis. “The Super Bowl is a case study in this.”

Society must make exercise easier to get, said Sallis, a professor of psychology at San Diego State University who studies environmental influences on physical activity. For instance, suburban communities built without sidewalks should install them, he said, so people can walk instead of drive.

And companies could review their mileage policies. “If you take your car on a work-related trip, your employer reimburses you,” he said. “If you walk or take your bike, nobody pays.”

Although the health club industry doesn’t track quitting on a month-by-month basis, club owners concede attrition is a continuing problem. Year after year, about one-third of all new club members don’t renew, according to the International Health, Racquet and Sportsclub Assn., a trade group.

Which means some members don’t last the year.

“By the Super Bowl, some people are done,” said Tim Rhode, owner of the Maryland Athletic Club and Wellness Center in Timonium. But the yearly losses work out to a monthly average of about 2 percent, and that amounts to a success for the industry, he said.

His club does better than the industry average — he loses “well below 20 percent” in the first year — but it works hard to fan new flame.

Any member who has not visited in 21 days gets a phone call. Rhodes says flagging members are offered “anything we can do to help them get started again.”

That’s best done delicately, said James Prochaska, an exercise scientist and director of the Cancer Prevention Center at the University of Rhode Island. “One thing you don’t do is pressure them into action,” he said.

Those who resolve to start exercising at the start of the new year often are ambivalent to begin with because they don’t know many reasons to continue to exercise, Prochaska said. The more reasons they have, the more likely they are to continue.

If a person continues through six months of exercise, it’s pretty much a habit, Prochaska said.

By that standard, beginning exercisers should forget about football’s Super Bowl and plan for baseball’s All-Star game. If they can make it to July 13, they’re hooked.