Who says you have to do squats to work your butt? This move targets your backside as well as your hamstrings.
Start by lying on your back on a yoga mat, with your knees bent and your feet flat on the floor. Your heels should be close to your butt and hip-width apart. Extend your arms at a 45-degree angle from your body, with your hands flat on the floor beside you.
Beginners: Push through your heels to bring your hips toward the sky. Then, lower your hips until they're hovering just above the floor. That's one rep; keep lifting and lowering for a total of 20 reps. Rest, and repeat.
Make it more challenging: To further engage your core, do the same move, but with your arms lifted straight into the air above your shoulders. Work up to doing 30 reps. Rest, and repeat.
Advanced: Place your palms back on the floor. Lift one leg straight in the air and keep it there while you lift and lower your hips. Keep your toes pointed and your core tight, and remember to push through your heels. Do 20 reps, switch legs, and repeat. Rest, and repeat one more time.
Tips: Don't lift onto your neck — keep your shoulder blades spread across the mat. Make sure your knees don't buckle out or cave in; they should be directly in line with your hips.