Deadlifts work the large muscles of your hips, but the degree of work depends upon your range of motion and the type of deadlift you perform. Your glutes provide power when straightening your legs or torso, and the smaller muscles of your hips control the rotation of your thighs. Consult a health care practitioner before beginning any strength training program.
During the deadlift, the amount of work your gluteus maximus -- the largest of the three gluteal muscles of your posterior -- receives, remains directly proportional to how far you get your hips down at the start of the lift. The more your legs have to straighten, the more you work your hips. Bend your knees and sit back with your hips before pulling the bar off the ground; this increases your work at the hip joint, which increases the work of your gluteus maximus.
The sumo deadlift works your glutes more than the conventional deadlift, according to a 2002 study published in "Medicine & Science in Sports & Exercise." By standing with your feet wide and keeping your knees pushed out, you also work the smaller gluteal muscles of your posterior -- the gluteus medius and gluteus minimus. Both of these small muscles control the rotation of your thighs. Keep them pushed out instead of allowing them to collapse inward as you pull the bar up to recruit these muscles.
The stiff-legged deadlift only fulfills half of the function of your gluteus maximus. As your knees bend very little during this exercise, the only work your hips perform remains helping you straighten back up from the bottom of the lift. While you can bend your knees more to achieve greater hip rotation, which would increase the amount of work your gluteus maximus performs, this also increases the strain on your lower back.
Increasing Your ROM
To increase your range of motion, or ROM, you can stand on a small platform, no more than 4 inches high. This will dramatically increase the work your hips perform. While this remains impossible when performing a sumo deadlift, you can load the bar with smaller plates to increase your range of motion. Keeping your torso as close to vertical as possible when pulling a sumo deadlift in this manner will increase the work your hips perform.