A great glute/buttocks exercise using the Pilates circle.
Lie on your back on the floor or on a yoga mat. Place the Pilates circle between your knees, keeping your knees bent to approximately 90 degrees. Your arms should be resting out to the sides.
Exhale and push into your heels to lift your buttocks off of the floor. At the same time, squeeze the Pilates circle with your thighs. Keep your core engaged at all times and avoid overarching your low back and also avoid shrugging your shoulders. Inhale and slowly lower your buttocks back to the floor, trying to keep your glutes engaged the whole way down. Repeat 8-12 times, rest, then repeat the entire exercise if desired.