The Sumo Deadlift offers various mechanical trade-offs as compared to the conventional deadlift. The wide stance of the Sumo Deadlifts allows the bar to positioned closer to the hips. The sumo position, along with the lower positioning of the hips, allows the torso to begin in a slightly more upright posture. Although this allows for a shorter moment arm between the hips and barbell, the lower position of the hips creates longer moment arms between the knees and hip.
The wide stances of the Sumo Deadlift also positions the body slightly lower to the ground thereby reducing the need to bend over as far. It could be said that the sumo stance decreases the distance the bar needs to be lifted but in effect it actually decreases the moment arm distances on the sagittal plane (< spine angle) while positioning moment arms more in the coronal plane (hip adduction). The legs push both outward and downward into the floor at lateral angles creating a converging reactive force driving the hips upward.
The Sumo Deadlift uses similar muscles as the Conventional Deadlift with a few notable variations. The Sumo Deadlift has a greater reliance on the powerful hip musculature with relatively less emphasis on the spinal musculature.
The wider stance and deeper initial squatting position relies heavily on the Gluteus Maximus and particularly the Adductor Magnus. Like the Squat, the hamstrings act as Dynamic Stabilizers moving through the hips and knee with little change in length. The hamstring may act as a Synergist nearer the top of the lift if the knees extend significantly sooner than the hips, which may be caused by a narrower sumo stance or long femura, possibly requiring the knees to be extended early in the upper mid position thereby permitting the bar to clear the knees.
Although the knees do not extend as far beyond the ankle with the wide stance with knees pointing outward, significant knee torque is still generated by the bilateral forces angled slightly outward and downward, eliciting quadriceps evolvement.
The Erector Spinae and their antagonist stabilizers, Rectus Abdominis and Obliques, while still heavily involved in stabilizing the spine are proportionally less evolved in the Sumo Deadlift due to the more upright posture of the torso as compared to the more bent over positioning of the Conventional Deadlift. This more upright posture also decreases the tendency for the spine to flex forward under the weight of a load.
The Sumo Deadlift is typically relatively easier nearer the top of the motion as compared to the Conventional Deadlift. However placing the arms narrower than shoulder width creates unneeded torque near the top of the motion potentially interfering with a full upright lockout since the bar cannot held as close to the center of gravity at the top of the lift with the arms positioned anteriorly on the body.