What does it say that my sumo DL is about 10%-15% weaker than my conventional stance DL? What muscles do I need to bring up to bring up my sumo DL.
Well, do you train both lifts equally? If you never do sumo in training it's normal that it is lower than your conventional. And maybe you are not using a proper sumo technique either.... it's not just a deadlift with wide feet.
I tend to rotate which stance I use. Generally I'll do two 4 week blocks conventional and one 4 week block sumo. So I go conventional probably 2/3 of the time. My thinking has been there are certain muscles that are underdeveloped (maybe hips?) or overdeveloped (maybe quads?) that could be leading to the difference.
My weak point in conventional tends to be off the floor as well, not sure if that plays in here at all.
It's actually a smart approach and you are right it leads to better muscle balance.
Your problem is either technical or could be that the hamstrings and/or glutes are not firing properly during the first inch of the movement. I would suggest a 4 weeks cycle of floating deadlifts.
Floating deadlifts are done standing on a 2" platform/surface (as if you were doing deficit deadlifts). But each rep starts with the bar 2" from the floor (so same position as it would be in your starting position off of the floor). Hold that position 1-2 seconds, making sure that it is the same as your regular starting position and are that your hamstrings and glutes are loaded. Then lift... lower the bar back down and pause 2" from the floor in a perfect position for the next rep.
Do this as your main deadlift movement for 4 weeks, could be conventional or sumo. I recommends 2 weeks of triples and 2 weeks of doubles. Doing 4-6 work sets that are challenging but done with perfect mechanics and positions.
Thanks. I'll give that a shot.