Tone up, slim down, and find balance with this high-energy summer workout from power yoga pioneer Beryl Bender Birch. It brings inner peace, a spiritual boost, and an unparalleled measure of serenity. But make no mistake: Yoga can also be a butt-kicking, sweat-inducing workout. We worked with Birch to choose eight power poses that build endurance, improve muscle tone, and invigorate you from head to toe. Warm up by doing a few sun salutations then try the following series, holding each pose for at least five breaths and focusing on using equal parts effort and relaxation.

What it does: Stretches the entire side of the body; strengthens the back and legs; relieves stiffness in the hips and backs of the thighs; improves digestion.

How to do it: Extend arms out to your sides at shoulder height and step feet apart so ankles are directly under wrists. Turn right toes out 90 degrees and left toes in 30 degrees. Bend right knee, bringing that thigh parallel to the ground, with knee directly over ankle. Reach your torso to the right and rest your right elbow on your right knee. (For more of a challenge, place right fingertips on the ground or on a block placed outside your right foot.) Extend left arm alongside left ear, rotating your left ribs up toward the ceiling. Look straight ahead or up, keeping your chin tucked into your armpit. Repeat to the left.

What it does: Opens the hips while building leg strength; promotes balance; sharpens concentration.

How to do it: Bend forward and put your hands on the mat by your feet, bending your knees if necessary. Lunge your right foot back, keeping your left foot front and left, feet at least hip-width apart. Draw your right hip forward and left hip back to bring your hips into alignment. Stack your left knee over your left ankle, being careful not to push your knee beyond your toes. Once you're stabilized, lift arms up alongside the ears, reaching your upper torso up and back slightly while keeping your hips low. To modify this pose, place back knee on the ground, sinking your hips toward the heel of your left foot. Repeat on the left side.

What it does: Opens the hips, chest, and heart while strengthening the back and legs; develops concentration.

How to do it: Stand with your feet slightly wider than hip-distance apart and hands on hips. Turn your right toes 90 degrees to the right. Bend your right knee and place your right fingertips on the ground about 12 inches in front of and just to the right of your right foot (right thumb is in line with your right pinkie toe). Or use a block. Slowly lift your left leg to hip height with foot flexed and extend your left arm along your left leg. Reach out through the top of your head and the sole of your left foot to lengthen your entire body. Gaze at the floor or, if you feel balanced, gaze at the horizon. If you're ready for more of a challenge, reach your left arm straight up and rotate your neck to look up at your left fingertips. To come out of the pose, slowly bend your right knee and lower your left leg to the ground. Repeat on the left.

What it does: Opens the front of the hips and the chest; strengthens the back muscles; promotes feelings of liberation. "It almost feels like you're levitating," Birch says.

How to do it: Stand with your feet together. Bend your right knee and lift your right foot toward your right buttock. Hold the top of your foot or inside of your ankle with your right hand. Extend your left arm straight out in front of you. To help you balance, find a spot on the horizon to gaze at and keep your focus there. Keep your chest, shoulders, and hips facing forward and your left leg straight and strong as you push your right foot into your right hand and lift your right leg up. Repeat on the left.

What it does: Strengthens the arms, shins, back, and quadriceps; stretches the Achilles tendons, calves, and triceps; increases range of motion in the shoulders. "Because this pose is so strengthening, it makes you feel empowered," says Birch. "It teaches you to stand on your own two feet when the going gets tough."

How to do it: Stand with your feet parallel and big toes touching. Extend your arms alongside your ears and bend your knees to lower your hips, as if you were sitting in an invisible chair. Press your knees together and draw your navel in. Encourage your shoulder blades to move down your back. Gaze forward at the horizon.

What it does: Strengthens the legs, arms, and shoulders; builds core strength; provides a great weight-bearing exercise for the arms.

How to do it: Start on your hands and knees with your hands directly under your shoulders. Step one foot at a time back to come into the top of a push-up. Make sure your body is one long line -- don't let your hips sag below or rise up higher than your spine. Push into the floor with your hands, pull your navel up, and reach back through your heels to get your entire body involved in supporting you. Do not lock your elbows in this pose. To keep the back of your neck long, look at a point on the floor just in front of your hands. If you need to, bring your knees to the floor.

What it does: Strengthens everything. "This is one of those poses that requires strength, which can be built over time," says Birch. "Work to find the balance between contraction and relaxation."

How to do it: Start on your hands and knees with your hands directly under your shoulders, your knees directly under your hips, and your toes tucked. Then, step your feet back so your legs are straight and only your palms and toes are on the ground. Keeping your elbows close to your sides, bend your arms to bring your chest forward and down to just a few inches off the ground. Keep your shoulders higher than your elbows. To keep your lower body energized, tuck your tailbone, lift up through your navel, and push out through your heels. If you find it too difficult to maintain this alignment, modify the pose by dropping your knees to the floor.

What it does: Opens the throat, chest, abdomen, pelvis, and fronts of the legs; massages the digestive and reproductive organs; energizes the body.

How to do it: Lying on your stomach, bend your knees and reach back with your hands to hold your legs just below the ankles. Press your legs into your hands and lift your head, chest, thighs, and feet. Tuck your tailbone and pull your belly toward your spine. Afterward, roll over onto your back and pull your knees into your chest. Give yourself a big hug to release your lower back.