1. The bottom line Here's the minimum you need to stay healthy: muscle-strengthening exercises twice a week plus 2 1/2 hours a week of moderate activity like walking. Or 75 minutes a week of a more intense activity like jogging. Ask your doctor before starting a new exercise routine.
2. Get fitter faster A more intense workout burns more calories in less time, says Pamela Peeke, M.D., author of Fit to Live. "You can walk a 5-kilometer [3.1-mile] race in 40 minutes, jog it in 30 minutes or run it in under 20 minutes. Either way, you're burning the same amount of calories," she says.
3. Short spurts are best Alternate spurts of hard, high-speed activity with periods of slower activity to shorten a workout while improving fitness, says Ron Woods, a coach at the Human Performance Institute in Orlando, Fla.
4. Stronger muscles in minutes We lose muscle mass as we age, making us weaker. Two or three 30-minute weekly sessions using free weights or resistance bands will restore muscle and keep bones strong, says David Sandler, author of Fundamental Weight Training.
5. Upper- and lower-body moves Alternating an upper-body strength training exercise with a lower-body move is a time-saver, says Gina Lombardi, author of Deadline Fitness, who has trained celebrities such as Andy Garcia. Alternate cardio moves, like rope-jumping, with strength exercises such as lunges.
6. No-sweat workout Even office workers can handle a 15-minute daily exercise break, says trainer Rick Bradley, who helps people train at work. Start with a 10-minute walk in the hallway or outdoors, then add a few exercises with resistance tubes and a couple of side bends. "The trick is to do this every day," he says.
7. Say yes to yoga A few minutes of yoga-type stretches after a workout improve flexibility, range of motion and strength in a way that aerobic activities can't, says Beryl Bender Birch, author of Boomer Yoga. An introductory class is best for beginners, since regular classes often last 90 minutes.
8. Buddy up Exercising with others makes time fly. Dodo Stevens, 67, of Portland, Maine, meets 10 women and a trainer for a 45-minute workout at a neighbor's house. Cost: $11 per person. "I love working out with other people," she says. "The whole thing is over before you know it."
9. Mix it up Exercise programs need variety. If you do the same thing all the time, your body adapts and you stop making progress, says Peeke, the fitness author. Look for classes that provide an introduction to Zumba, Bellyrobics or other new, fun activities.
Elizabeth Pope is a writer based in Portland, Maine.