Because, as we all know, it’s totally possible to lift more weight without “activating” more muscle. Cuz “levers”. Or maybe magnets. I dunno.
I'm probably whistling in the wind responding to this, but my goal is to provide information to the rest of the forum members who have an interest in this topic as opposed to trying to convince you.
First, I owe a "thank you" to Mark Rippetoe. I've criticized him about his views on the low bar squat and he told me I was wrong. He then sent me a free copy of his book and told me to read the squat chapter to see why I was wrong. So thanks for the book. I did read the squat chapter, and it is probably one of the most detailed explanations of the squat I've ever read. Mark clearly has a passion for this stuff. The other reason I need to thank him is that while researching this issue, I've learned a ton of information about the squat - stuff I probably would not have learned otherwise.
So, after reading the squat chapter, have I changed my mind? No, and I'll explain why.
Mark analyzes the squat based on moment arms. He states that placing the bar lower on the back allows us to use a more horizontal back angle. This more horizontal back angle, in turn, creates a longer moment arm at the hip, which requires the hamstrings to work harder in the low-bar squat. From a pure
physics standpoint, he is correct. However, things are different when you look at this from a
biomechanics standpoint. I'll come back to this.
One thing that Mark does not mention is that placing the bar lower on the back, while lengthening the moment arm at the hips,
shortens the moment arm for the knee extensors - the quads. This creates a leverage advantage for the quads, which means the quads now need to produce less force to move the same amount of weight. This one of the reasons why most people can lift more weight with the low-bar squat. The quads are able to move more weight by producing the same amount of force as in a high-bar squat, more or less. So yes, despite the sarcastic leverage comment from
@Bill Been the low-bar squat does in fact create a leverage advantage for the quads. Magnetic fields are optional.
But what about the longer moment arm for the hamstrings? This is where biomechanics comes in. If the hamstrings only function was to extend the hip, then I wouldn't be typing this post. Mark would be 100% correct and the low-bar squat would be superior in all respects. However, the hamstrings cross two joints - at the hip and the knee. They are responsible for hip extension
and knee flexion. Knee flexion is when you bring your heel to your butt and knee extension is when you move your heel away from your butt, i.e., straighten your leg. The quads are responsible for extension. This means that the hamstrings and the quads are antagonists - their actions conflict with each other. What would happen if your quads and your hamstrings contracted maximally at the same time? Nothing. Your leg would not move at all. Fortunately, our nervous system has found a way around this problem so that the two muscle groups can work together without interfering with each other - it's what allows us to walk. However, even with this nervous system magic, the two muscle groups still cannot
maximally contract at the same time. For purposes of the squat, the quads are the prime movers doing the brunt of the work. The hamstrings function to stabilize the knee. Near the end of the lift when the lifter is close to standing straight up, the quads' work is mostly done and the hamstrings can kick in a bit more to extend the hip and allow the lifter to stand up straight. So there is no question that the hamstrings are involved in the squat, and they are probably involved a bit more in the low-bar squat given the more horizontal back position. However, the realities of biomechanics prevent the hamstrings from being involved to such a degree as to make the squat a good hamstring exercise.
But what about the fact that your entire body is supporting more weight in the low bar squat? Leverage and biomechanics cannot magically make the bar lighter. This is true, but how much more weight are we talking about? I've said this before and I'll say it again - most lifters can use about 5 to 10% more weight in the low-bar squat than in the high-bar. So, if your normal working weight on the high-bar squat is about 200 lbs., you should be able to use about 10 to 20 lbs. more in the low-bar. This additional weight is shared by the quads (which have a leverage advantage), the lower back, the glutes, and to a small extent the hamstrings. These are the strongest muscles in our bodies. How much stronger are these muscles going to get if they
share the work of moving an additional 10 to 20 lbs.?
But what about the fact that some lifters experience soreness in the back of their legs after a squat session? I've experience this myself and I squat high-bar only. The question is whether experiencing "soreness in the back of the leg" indicates soreness in the hamstring, which would mean they worked hard, or soreness in some other muscle that is located near the back of the leg? It's the second one. The adductor magnus is a large muscle that contributes to hip extension. It is likely that the soreness felt after a heavy squat session is coming from the adductor magnus rather than the hamstrings.
Adductors
If you like to low-bar squat for general strength training, go for it. I have no problem with that. However, if you're using the low-bar squat to strengthen your hamstrings, you're using the wrong exercise. With the possible exception of the box squat, no squat is ever going to be a good hamstring exercise. Period.
