This is just an informative post in which I try to clarify the trade-offs between the conventional and sumo deadlifts. I was watching some deadlift videos on youtube and some of the comments I read were just plain stupid. I have nothing against either lift. I have personally switched over to sumo deadlift because it’s a more favorable back angle for my thin mid section and I can pull heavier. I still train both.
I believe people should do whichever they feel they are strongest at. The comment that annoys the shit out of me is people saying that sumo deadlifts are way easier than conventional deadlifts. Let’s get into the mechanics of conventional vs. sumo to see what the actual trade-offs are.
For simplicity, I will only analyze the lower body portion. We can discuss the back angle, moment of inertia in the mid section, and bending moment experienced in the upper body if need be. By analyzing the legs using a free body diagram, we can determine the difference in work and the amount of force generated in the legs for both styles. The angle of the legs relative to vertical will be defined as Theta. Work is equal to force x length.
For conventional, Work = Weight x Distance. For sumo, the distance traveled is Distance x cosine(Theta). So for sumo, Work = Weight x Distance x cosine(Theta). I think everyone knows this portion. Now here’s the second part of the analysis that most people forget, the force generated in the legs. For conventional, the force in the leg is about equal to the weight being pulled since the force is applied in the same direction that the weight is moving (up), that means Leg Force = Weight.
For sumo, the force is applied at an angle so in order to move the weight up, more force has to be applied compared to the weight. This means that Leg Force = Weight x secant(Theta). We can turn these numbers into ratios to see the relative comparison.
Sumo / Conventional = cosine(Theta)
Leg Force Comparison
Sumo / Conventional = secant(Theta)
For me, I have a leg angle of 25 degrees. So by switching to sumo, I reduce work by 9.4% but increase leg force by 10.3%. For some people who use a wider angle of 30 degrees, they reduce work by 13.3% but increase leg force by 15.5%. I want to point this out that even though a person does less work doing sumo, they have to generate more force to do less work.
That is why you see a split between styles for world record holders. They do what is advantageous for them while still being within the powerlifting rules. The graph at the top shows how work decreases and leg force increases with respect to the leg angle (ranging from 0 to 90 degrees or 0 to 0.5Pi).