The stiff-legged deadlift with dumbbells increases the development of the quadratus lumborum which aids in the side to side movements of the lower back including the spine. Improvements in the range of movement within the hip joint as well as flexibility for the hamstring muscles can be seen as well.
Muscles Targeted: The main focus of the dumbbell stiff leg deadlifts are the muscles of the lower back including the quadratus lumborum that causes the lateral movement of the trunk and the lumbar spine, the hamstrings (back of the upper leg), latissimus dorsi (upper back), as well as the arms and forearms.
How-To: Find a comfortable dumbbell weight to start with and hold a dumbbell in each hand with your arms hanging straight down in front of your body. The legs should be shoulder-width distance apart with the toes pointing forward or slightly to the side. Begin this movement by bending at the waist and lower the dumbbells to below knee level or lower. Be sure to keep your legs slightly bent at the knee and stick your butt out as you descend. Be sure to to keep your back straight and taught to let your back and leg muscles do the work.
Important: Keeping the entire back flat for the whole duration of the dumbbell stiff leg deadlifts is very important. Look forward so the chest, shoulders and chin are in a neutral position.
Reps and Sets: Stiff-legged deadlifts with dumbbells can be used to help improve muscular endurance by training within 15-20 repetitions for 2-3 sets. To improve muscular strength do 10-12 repetitions of 3-5 sets. For increased muscular power do 5-8 repetitions of 4-5 sets per workout.
Personal Trainer Joe Tong in Golds Gym in Venice, California, shows you the proper way to do stiff-legged deadlifts with dumbbells in this video.