Our Better-Butt Challenge [1] has 21 days of workouts to help you take your butt from flat to full. In the end, you'll have a tighter, stronger backside. Be sure to check back tomorrow when we share the next workout of this three-week plan.

Welcome our Better-Butt Challenge! Good news: for today's workout, all you need is a mat and your floor. We like to call this our Lazy-Girl Workout because you don't even need to stand up, but don't be fooled — your backside will feel worked, and you'll be proud that you're already done with your workout for the day.

Directions: do two rounds of this complete eight-exercise circuit. Stretch your back with Child's Pose [2] as needed throughout the workout.

Week one, day three: eight reps

Week two, day 10: 10 reps

Week three, day 17: 12 reps

Bird Dog

• Begin on all fours with your hands directly under your shoulders and your knees directly under your hips. Bring your abs to your spine as your bring your left knee and right elbow together under your torso.
• Keeping your torso stable, straighten your right arm and left leg. Reach through your left heel to engage the muscles on the back of the leg and your butt.
• Return to starting position and switch sides to complete one rep.

Clam

• Start by lying on your left side. Bring your knees and hips to a 45-degree angle bend. Position your top pelvis away from your head to bring your waist off the floor. Maintain this neutral position throughout the entire exercise.
• Lift your top knee up, keeping your heels together. Lower back to starting position, ensuring that you're not moving your pelvis or torso.

Single-Leg Bridge

• Lie on your back, and bring your left knee into your chest with your hands clasped just below your knee. Lift your right toes up, and press your right heel into the floor to lift your pelvis and torso off the floor.
• Lower your back and pelvis to the ground to complete one rep. Switch sides after finishing all your reps on the right.

Donkey Kick Pulses

• Begin on all fours and lift your right leg off the floor until your knee is in line with your hip.
• Flex your foot and squeeze your glute to raise your heel an inch toward the ceiling. Continue these small, concentrated pulses.
• Open your right knee out to the side, keeping your foot flexed, and pulse your leg one inch to the left. You are not trying to lift the knee up, but try to keep it level as it moves behind you. You should feel your glutes firing away as you pulse.
• Repeat on the other side to complete a set.

Elbow Plank With Side Step

• Start in an elbow plank.
• Extend your left leg out to the side, gently tapping your toes on the ground.
• Bring your foot back into a plank. Repeat the same movement with your right leg to complete one rep.

Superwoman

• Lie face down on your stomach with arms and legs extended. Keep your neck in a neutral position.
• With your arms and legs straight (but not locked) and torso stationary, simultaneously lift your arms and legs up toward the ceiling to form an elongated "u" shape with your body — your back arches and arms and legs lift several inches off the floor.
• Hold for two to five seconds and lower back down to complete one rep.

Elbow Plank With Donkey Kick

• Begin in an elbow plank with elbows directly under shoulders, abs engaged toward the spine. Don't let the pelvis sag down or pop up.
• Lift right leg off the ground, bending your knee so the sole of your foot is toward the ceiling. Keep pelvis square to the floor. Don't let your pelvis twist.
• Press your right heel toward the ceiling as high as you can without moving your pelvis or lower back. The motion will not be huge but rather concentrated on the booty and hamstring.
• Lower the bent leg slightly; repeat this motion for the required number of reps, then switch sides

Tabletop Bridge

• Sit on the mat with your fingers facing away from you, with about 12 inches between your butt and your heels.
• Press through your glutes as you lift your butt off the floor, coming into a tabletop position.