Steve Rosenthal likes to exercise but has a killer schedule. Besides being on the road constantly as a print salesman, the 49-year-old father has another full-time job--chauffeuring his sons to hockey, lacrosse, and baseball practices and games.

So Rosenthal has worked out his own exercise plan. While driving, he tightens his stomach and holds for ten seconds 30 times and then takes one foot off the floor mat very slowly ten times. "I get a caloric burn and strengthen my stomach and legs rather than just sit on my rump," he says. Between games at a hockey rink, Rosenthal will go for a walk. "If I'm giving up exercise for my kids, I try to make it up some other way during the day."

Susan Hackley also has a heavyweight schedule. When she takes the elevator to her fifth floor Cambridge, Massachusetts, office (and she's riding solo), Hackley will bend her knees and do figure eights to warm up her joints, an exercise she learned in a tai chi course. At more ambitious moments, she will skip the elevator and take the stairs or park far away from her building and walk.

Recently, Pauline Field found herself in a Chicago hotel room after a long plane ride. She knew she would be sitting in cabs and eating out too much, so she did three repetitions of 15 lunges from her hotel door to the window.

Emily Tufeld stores two five-pound bar bells in her Tarzana, California, bathroom and keeps her arms in shape while she waits for her bathtub to fill.

Rosenthal, Hackley, Field, and Tufeld are part of a growing group who exercise a few minutes at a stretch throughout the day rather than in one intensive 30 minute to one-hour session. For busy people--and who isn’t?--it makes a lot of sense. According to Joan Price, co-author of The Anytime, Anywhere Exercise Book, "The immediate result is that your mental and physical energy goes up so you're more productive. Long term, the risks of heart disease, diabetes, and many forms of cancer go down when you accumulate 30 minutes of moderate activity a day."

Why? You reap health and weight loss benefits by burning about 1,000 calories a week in extra physical activity. That's equivalent to 30 minutes of moderate exercise six days a week. And it requires no heavy lifting. Price's book offers exercises that can be done in the shower, while a Web page slowly loads or the copier finishes, in the grocery line, at the airport, or in other everyday venues. Remember: The more minutes you move, the more calories you burn during the day.

Do sweat the small stuff
"The exercise needs to be somewhat demanding," maintains James Labadie, a fitness trainer, owner of Achieve Total Fitness in Tampa, Florida. "As long as it is challenging, the body will respond with increased muscular strength, endurance, and tone." Debbie Mandell, a personal trainer and author of Turn On Your Inner Light: Fitness for Body, Mind, and Soul, says that by walking just a few minutes, you burn off the stress hormone cortisol and shed that lunchtime slump.

Of course more is better, but a lot depends on your objectives. The Institute of Medicine last year urged 60 minutes daily of moderately intense activity to gain the full health benefits of exercise and keep down weight. But the American Heart Association believes just 30 minutes most days will decrease the risk of disease and increase longevity. And the American College of Sports Medicine agrees, particularly for people who are out of shape.

The skinny on exercising
Three types of fitness--aerobic, also called cardiovascular, muscle strength training a.k.a. resistance training, and stretching--complement one another so strive to do them all during the course of a week.

• Experiment with abdominals. Do crunches on the floor, if possible. When sitting or standing, try isometric abdominal contractions. Pull in abs slowly and release but keep them partially contracted. Repeat.
  
  
• Stretch your back. Stand and hold onto something sturdy (a fence, railing, or chair) at waist level. Round your back, sinking your weight back so that you're stretching your back.
  
  
• Master push-ups. Your first choice should be the floor, but if you're not strong enough, use a desk or counter. Keep body in a straight line, abs tight, no sinking at stomach or hips. Bend elbows to lower body (inhale), then straighten arms to raise body (exhale). Or try wall push-ups, changing hand position from wide to close together to target muscles from different angles.
  
  
• Learn to love squats. Do them with weights, exercise bands, or your own body weight. Stand up straight, lower body as if you're going to sit in a chair, keep body weight over heels and back neutral. Don't let knees go forward of toes. Squeeze buttocks as you straighten up.
  
  
• Use trainer Simma Lieberman's 2-for-1 strategy: Exercise at the same time that you're doing something else productive, e.g., walking and talking business on a cell phone, listening to work-related material on CD or tape while walking, running, or doing other exercise. If you're put on hold, use speakerphone and do yoga or stretching.
  
  
• Take active breaks often. Run up and down stairs if you can't get out. Don't sit if you can stand. Don't stand if you can pace.
  

Sally Abrahms sucks in her abs on all occasions--at her desk, during movies, and especially when the dog takes her for a walk.