What specific routine you choose depends on your preferences and babysitting options.
For a cardiovascular workout, an aerobic class, a session on the StairMaster or elliptical trainer, or following a video in the comfort of your living room while your baby naps are all good choices. Whatever aerobic exercise you choose, start slowly. For example, if you're using a machine, work at a low level until you're feeling comfortable with the movement or exercise, suggests Cunningham. Then gradually step it up.
If you can't find an uninterrupted 20- or 30-minute stretch in your day, don't give up; just shoot for two or three shorter sessions. Research shows that you'll burn the same amount of calories whether you work out for 30 minutes continuously or in three segments of 10 minutes each, says Carla Sottovia, assistant fitness trainer of the Cooper Fitness Center in Dallas. However, you won't get the same cardiovascular benefit if you don't exercise continuously. During the course of a day, you should be able to find a few opportunities to walk around the block, march in place, jump rope, or complete a short segment of an exercise video.
You can accomplish a top-to-bottom muscle workout in 10 to 15 minutes if you focus on multijoint moves that work more muscles, such as lunges, squats, pushups, and biceps curls. One set of about 12 to 15 repetitions should do it, as long as you work your muscles to fatigue -- meaning you can barely squeeze out the last rep or two. When you're really pressed for time, you can combine two moves in one exercise, such as doing biceps curls while you lower yourself into a squat. Just be aware that dividing your attention may make that workout less effective, says Neporent, because you may not focus on one form as well.