I want to work out, but on many days I have only 10 to 15 minutes to spare. Is it worth exercising for such a short amount of time?

Absolutely! With everything else going on in our lives, exercise often falls to the bottom of our to-do list. But you don’t need to spend a lot of time in the gym to get strong and fit. In fact, our research shows that you can get significant results by doing just five minutes of strength training three times each week. The key: doing exercises that work several muscles at once. And you really need to do only one set, which the American College of Sports Medicine has concluded is just as effective at building muscles in beginners as two or three sets. Do one set of leg presses (targets quads, hamstrings, glutes and calves), one set of bench presses (works shoulders, chest and triceps) and one set of seated or bent-over rows (tones upper back, rear shoulders and biceps). Do each rep slowly, which will make you use your muscles instead of momentum. Aim for one set of 10 to 15 reps of each exercise, which should take about a minute, then follow each set with a minute of rest. If you have a few extra minutes, add a set on the overhead press machine, which strengthens the rest of your back and shoulder muscles, and the low-back extension and abdominal-curl machines to firm up your core muscles. Be sure to let your muscles rest for a day before doing the routine again, and of course, always check with your doctor before beginning any exercise regimen. And on the days you can devote a bit more time, park your car 5 to 10 blocks away from the gym and walk briskly. That should add 10 to 20 minutes of aerobic activity to your workout.

Expert Wayne Westcott, Ph.D., is a fitness research director at the South Shore YMCA, in Quincy, Mass.