Tim, first I want to say thanks for taking the time to set up this forum so we can all share our thoughts and learn more about the deadlift. It also speaks volumes about you as a coach that you have no problem sitting down and debating over material that you have published.
I do agree that all of those movements are involved in a deadlift, just obviously during different portions of the lift.
Trunk and Spine Extension: I donâ??t know if these two actions can be separated, and I donâ??t think they occur past the set-up phase of the lift. If the lumbar spine extends at all during the lift it is a miniscule amount. This also has to be considered segmentally, because there are different actions at the cervical, thoracic and lumbar sections of the spine. But, of course the erector spinae (longissimus, iliocostalis, spinalis) as well as the transversospinal muscles such as the multifidi are involved in spinal and trunk extension. The lats, rhomboids and traps also aid the spinal erectors in generating the initial spinal extension during set-up and help to finish the pull.
Hip Extension: I believe that this is the predominant movement of the deadlift. While the deadlift is a full-body lift, it is a hip dominant pattern. The movement is primarily generated by the glutes and hamstrings with the erector spinae acting as an assist.
Knee Extension: This is the initial movement of the deadlift and is generated predominantly by the quads.
My main point of contention is that the spinal erectors are the agonists of the deadlift. Do I disagree with the fact that they are extremely active throughout the lift? Hell no. That being said, I donâ??t believe they are the driving force behind the deadlift.
I spent a lot of time thinking about this after I approached you and I also had a conversation with Smitty from the Diesel Crew, I have the privilege of training with him on Sundays and we happened to be deadlifting, but the prime mover changes throughout the course of the deadlift. Initially, the agonists are the quads because they are generating the force to get the weight moving off of the ground, but as the joint angle and angular velocity changes so does the prime mover. Once the knees extend past a certain point, the glutes and hamstrings become the prime movers to create the hip extension to lock out the weight. Although the back is very active throughout the lift it is so the hips can do their job. Like I stated above, there is very little extension in the lumbar spine throughout the lift and most of it is to maintain the neutral spine position.
In the thoracic spine there is virtually no extension during the lift. There may be some at during the final pull, but most if that is generated by a powerful lat contraction; further leading me to believe that the spinal erectors are not the prime mover or agonist.
Iâ??ll use a quote from Dr. Stuart McGill. If there is a better authority on training the back and its function during movement I would love to meet him. Here goes:
â??Power (force times velocity) should come from the hips. The risk rises when power is developed in the spine. The implication is that when high spine torques are developed, the velocity of spine motion be low. Conversely, high spine velocity is safe only when the torques are low. Weightlifters develop enormous hip power but virtually no spine power (high force and low velocity) because the spine is locked into a static position while the high velocity angular motion is provided by the hips.â??
While much of that quote is devoted to Olympic lifting, all Oly lifts start with a deadlift. And while the velocity of a deadlift, especially a maximal effort, is much less than Olympic lifts, there is still a great amount of torque. Not to mention one of the most common movement distortions seen today involves over-active spinal erectors and weak or inhibited glutes. So, training the erector spinae to be the prime movers would seem like a mistake.
Considering all of this, it seems very logical to believe that while there are multiple prime movers during the deadlift the spinal erectors arenâ??t one of them.
Your thoughts?
Reference
McGill, S. (2009). Ultimate back fitness and performance: fourth edition. Waterloo: Backfitpro Inc.