Don't misunderstand my POV, I'm not advocating a lot of flexion/rotation or even a little. In practice I strongly believe one should strive for a neutral spine, whatever that is understood to be by the individual within a common sense definition (know it when you see it).
Excellent
While I'm unwilling to pay for access to the referenced McGill study, some web crawling revealed it has been linked in several discussions about flexion under load, I have no reason to disbelieve the numbers. That said, nowhere was it stated McGill being OK with that amount of flexion, or that the 40° was an average - probably an outlier cited for dramatic effect in the article(s). It was stated that people coached to perform these movements executed them under McGill's direction and observation and that is what he recorded.
It's not the numbers I disbelieve, but the context in which the numbers are being understood. For example, this quote from the article you posted:
“Even when participants are cued to execute the movement with a neutral spine (and under careful observation by experts such as Dr. Stuart McGill), we still see lumbar flexion occur. Within a
squat, there is 40° of flexion occurring, 26° of flexion during a
kettlebell swing, and 25° of flexion during a
good morning. This elucidates the point of neutral spine being more a range than a specific position. If during most
“functional” movements we see the spine flex up to approximately 40°, then what exactly is the neutral zone?”
I found the original papers Sam Spinelli is quoting from. Enter their titles into Google Scholar and there they are. In reference to the squat reaching 40 degrees of lumbar flexion, the following quote from the original article:
"The subjects did two types of lifts in the sagittal plane: one in which they bent predominantly at the knees with the trunk slightly flexed and the other in which they bent predominantly at the trunk with the knees slightly flexed. For the purposes of classification these where called "squat" and "stoop" lifts, respectively"(1).
I must interject here by saying nowhere in this article does it say that the authors taught their subjects to lift with a neutral spine (sorry Mr. Spinelli). The purpose of the paper as stated at the end of its introduction "was to examine the interplay between muscular and ligamentous sources of extensor moment and the resultant loading of the L4-5 joint by comparing lifts with varying degrees of trunk segment flexion"(1). They then had subjects lift varying loads under 32.4kg with each technique-no neutral spine involved. The authors noted this was under the "maximum permissible limit" of 6400 N set by OSHA (1). This article is about which lifting technique causes more stress to the L4-5 segment. They are merely studying different ways people commonly pick things up. I can say that clinically I have seen people injured both ways, but the stoop lifting technique more commonly appears to cause injury, which coincides with their findings. In the results section they state that with the squat technique people were reaching 40 degrees of lumbar flexion with only 64 degrees of trunk flexion total. So Mr Spinelli grabbed that number and ran with it-out of context. The authors conclude "the risk of injury may be influenced more by the degree of lumbar flexion rather than the choice of stoop or squat technique" (1).
Regarding the reference to good mornings causing 25 degrees of lumbar flexion. I can find no reference in the original article on how the subjects were coached (2). Once again, I do not doubt the numbers. I doubt the self awareness of the subjects and their ability to maintain a neutral spine, truly hinge through the hips, and stop before lumbar flexion occurs.
In the article on the kettlebell swing, it DOES state that the subjects (all whopping seven of them), were coached to get the kettlebell swing and snatch right before starting the study. They were also instructed to maintain a neutral spine. They obviously didn't maintain it throughout the swing/snatch, because they did show 26 degrees of lumbar flexion to 6 degrees of lumbar extension throughout the move. And this makes perfect sense if you take somebody who walks with an anterior pelvis (most people these days), coach them briefly in a dynamic move, and then study them. Learning to maintain a neutral pelvis, which translates into a neutral spine, takes time. To do it dynamically is even more advanced. My thoughts, they had a neutral spine to start, once they got swinging, their pelvis failed to maintain neutrality and this led to increased lumbar movement. They were likely amateurs (or they wouldn’t have needed coaching to begin with), as
@Brett Jones alluded to. If McGill had studied 7 SFGs, would the results be the same? Pavel was included in this study, but his results are discussed separately and his lumbar flexion angles are not mentioned (3).
Continuing from the discussion section of the article on the kettlebell swing:
"From another perspective, nearly all people who develop painful back conditions have movement flaws. Perhaps the most common is to move the spine when it is under load. Repeated compression of the spine while it is bending is the mechanism that leads to eventual disc bulges although this is modulated by disc size, shape, the magnitude of accompanying compressive load, to name a few variables (a synopsis of this literature is found in McGill [14]). The spine can withstand high loads if it is postured
close to its neutral curvature. The ‘‘corrected movement pattern’’ requires ‘‘hip hinging’’ to bend and lift. This is incorporated in kettlebell swings with good form—that being hip motion rather than spine motion" (3).
So, do folks commonly show these lumbar angles when they lift. Yes. Is it optimal or ideal. I don't think so. Would time and more coaching reduce it. I think so. Truthfully, I think Mr Spinelli took some liberties in assuming the flexion angles stated represented a neutral range. None of the these papers state that the lumbar flexion angles shown in the lifts studied fell within a neutral range.
Personally, I don't think 25 degrees of flexion is close to a neutral curve. And, the neutral range likely varies by individual.
Thanks for the discussion. These long posts get muddled. I hope I make sense.
Sources:
- Potvin JR, McGill SM, Norman RW. Trunk muscle and lumbar ligalment contributions to dynamic lifts with varying degrees of trunk flexion. Spine. 1991;16(9):1099-1107.
- Vigotsky AD, Harper EN, Ryan DR, Contreras B. Effects of load on good morning kinematics and EMG activity. PeerJ. 2015;6(3):e708.
- McGill SM, Marshall LW. Kettlebell swing, snatch, and bottoms-up carry: back and hip muscle activation, motion, and low back loads. J Strength Cond Res. 2012;26(1):16-27.
