Your knee position when deadlifting depends on your flexibility and the type of deadlift you perform. For most types of deadlift, you wish to keep your torso as close to vertical as possible. This reduces the strain on your back but means your knees must flex more. If you have a specific knee issue that deadlifting aggravates, do not perform the lift without the approval of a health care practitioner.
Knees
When deadlifting, a direct relationship between the angle of your knees and your ability to maintain a vertical torso exists. The more you bend your knees, the more your hips come down, and the lower your hips at the start of the lift, the less you strain your lower back. This technique can apply to both the conventional and sumo deadlift. This technique does not apply to the stiff-legged deadlift.
Conventional
The conventional deadlift requires you to stand with your feet no wider than your shoulders. With your shins touching the bar, the closer you get your torso to vertical, the more your knees will flex. If you sit back with your hips and get your shins closer to vertical before pulling the bar off the floor, your knee angle remains less acute than if your ankles flex. The more you flex at your ankles and the less you flex at the hips, the more you strain your lower back.
Sumo Deadlift
Standing with your feet nearly out to the plates of the barbell, with your toes turned out changes your knee position. The sumo deadlift allows you to use more leg drive than the conventional deadlift, which reduces the stress on your lower back, according to a study published in the 2000 issue of "Medicine and Science in Sports and Exercise." Because your ankles do not flex forward and your shins do not get close to vertical, the sumo deadlift allows more leg drive with a less acute knee angle than a conventional deadlift with your hips low.
Stiff-legged Deadlift
The stiff-legged deadlift remains exactly that -- a lift where your knees stay stiff. Stiff does not mean locked, your knees should stay slightly bent throughout the lift. For the stiff-legged deadlift to effectively stress your hamstrings, which remains the goal of the exercise, you must bend at the hip and nowhere else. Your knee position here should remain as close to straight without locking out during the exercise.
References
- "The Westside Barbell Book of Methods"; Louie Simmons; 2008
- "Medicine and Science in Sports and Exercise"; A Three-dimensional Biomechanical Analysis of Sumo and Conventional Style Deadlifts; R.F. Escamilla, et al.; July 2000
