The shorter workouts won't build pro football muscles, but they will let an ordinary person build strength and stay strong. And if more people fit exercise into their lives on a reduced regimen, experts say the result is a net benefit for society.
"Something is really better than nothing. If I come in and I can work out vigorously for 30 minutes, I would consider giving it a try," said Dr. William L. Haskell, an exercise researcher and professor of medicine at Stanford University.
The express workouts typically require only one set of 8 to 12 repetitions instead of the 2 or 3 sets of 8 to 16 repetitions that physiologists recommend for an optimum workout.
Resistance exercise doesn't have to take much time.
"Most of (the time) tends to be spent moving from one exercise to another, or resting between sets," said Russell R. Pate, associate dean for research at the Arnold School of Public Health at the University of South Carolina.
Among the places at which shorter sessions are promoted is the Town Sports International chain of about 130 clubs on the East Coast. TSI says its XpressLine workout can be done in about 20 minutes.
When the shorter workout was tested against a traditional regimen, 78 percent of the 21 people on the shorter workout stayed with the program for two months, vs. 57 percent of the 14 people who tried the traditional program, said Wayne Westcott, who ran the test for TSI.
Those in the shorter workout also gained about twice as much muscle, said Westcott, fitness research director at the South Shore YMCA in Quincy, Mass. He speculated that people worked harder in the shorter program, although he said it would take follow-up research with more exercisers to prove the program's benefit.
TSI's is far from the only such program. Short workouts also are featured in chains such as Healthy Inspirations, which promises an aerobic and strength workout in less than a half-hour.
Healthy Inspirations markets primarily to women, and women don't have time for long gym programs, said Casey Conrad, the chain's chief executive officer.
"They've got the kids, the job -- they kind of shuffle everything," she said.
Consumers Union also has gotten into the act. The November issue of its newsletter Consumer Reports on Health outlines a six-exercise routine including biceps curls and crunches that can be done in as little as 25 minutes a week.
"It's not because studies are showing that briefer exercise is better than longer workouts," said Ron Buchheim, the publication's deputy editor. "It's driven mainly by the fact that, when you give people demanding workouts that may be optimal for health, they are so draining in terms of time and energy that people don't do them."
Shorter workouts are the top fitness trend predicted for 2004 by the American Council on Exercise, an organization which certifies fitness instructors.
Trainers will have to provide simple programs with simple equipment, so people feel they can accomplish what they want without investing too much of themselves in the effort, ACE said.
However, resistance training has yet to show it will provide health benefits that aerobic activity does, said Dr. Tim Church, medical director of the Cooper Institute, a health research organization in Dallas.
To reduce the risk of dying early, people should do at least 150 minutes a week of at least moderate aerobic activity such as a brisk walk, Church said.
Resistance may well be shown to have similar value, but "what we are rock solid on is that, with aerobic exercise, you gain tremendous health benefits -- n the magnitude of quitting smoking," Church said.