An added plus: You don't need to know how to swim to reap the benefits of water exercise (you don't have to get your hair wet, either). "Just moving in water is like lifting liquid weight," says Sanders. The more effort you use, by bumping up the intensity of a particular move, or using resistance tools such as dumbbell-shaped paddles or webbed gloves, the higher the resistance.
Water-exercise also forces you to strengthen your trunk muscles -- especially the abdominals and lower back -- almost without trying. That's because you must contract and use these muscles in order to stabilize yourself as you move. "Performing abdominal exercises on land, while you're lying on your back, doesn't prepare your muscles for the way you use them in real life," notes Sanders. In the water, you work them in an upright position by simply walking through the water.
The following workout, designed by Sanders, is so gentle that even a beginner can do it (although if you didn't exercise before your pregnancy, be sure to ask for your physician's approval). Get into the water and warm up for five minutes, swimming laps or just walking back and forth across the pool. Then, alternate these four strength-training moves with aerobic intervals. For instance, walk or jog as quickly as you can for 15 seconds, then go at a slow recovery speed for 15 seconds (as you get stronger, increase the duration of the high-intensity intervals). Alternate back and forth for 3 minutes. Then do move #1. Do another three-minute aerobic interval and do move #2, and so on. The workout should take about 30 minutes.
The buggy pushTargets the trunk, upper back and shoulders
Hold a kick board so it's up on one edge and immersed halfway into the water. Now walk while pushing the kick board in front of you. Concentrate on keeping the board straight. Turn around and walk back to the starting position, but this time zig-zag the board in front of you.
Lifting the babyTargets the arms
Stand with your elbows bent, palms facing up, floating on top of the water, (to make this even more challenging, wear webbed gloves to increase resistance or use water paddles). Bend your knees and lower your body into a squat position. At the same time, pushing your hands (or the paddles) down through the water until they're in front of your thighs. Rise up to the start position, curling your arms up toward your shoulders. Repeat 12-15 times.
Step climbTargets the buttocks and legs
Stand in the shallow end of the pool facing the stairs. Step up onto the lowest step and then back down. Repeat 10 times, slowly, leading with the right leg, and then 10 times leading with the left. Now turn sideways, so the stairs are on your right, and step up, leading with the right leg; repeat with the left. Finally, turn away from the step and step up backward, again, 10 times leading with the right leg and 10 times with the left.
Charlie Chaplin walkTargets the middle and upper back
Tuck your elbows into your sides, hold your hands out to the sides with your thumbs pointing up. Walk the width of the pool twice forward and twice backward.