I'll contribute, not to debate the issue, but to add my version of things learned directly from Mark Rippetoe and the SS teaching staff at a recent Starting Strength seminar.
First I'll caveat that I'm nowhere near a proficient Oly/weightlifter -- I can power clean and power snatch a barbell (about 125 lb and 95 lb, respectively) but I'm a real beginner with these lifts and don't know if I'll ever really pursue them beyond learning to do them so that I can teach them to others. I'm a lot farther along on powerlifts/strengthlifts - squat, bench press, overhead press, and deadlift with a few years' experience. Have been fortunate to attend both StrongFirst SFL and Starting Strength seminar so I have probably a unique perspective on both teachings. However, neither one of these teaches Oly/weightlifting.
The reason Starting Strength uses the LBBS is that they select for exercises that 1) use the most muscle mass and 2) provide the ability to move the most weight 3) over the greatest effective range of motion. Segment length and angle are the two things that affect moment force on a joint (and therefore the amount of muscle mass recruited), so the greater moment arm on the hip angle when you bend over farther for the LBBS means more muscle is recruited, and therefore more weight can be moved. Most posters in this thread agree that a few more pounds on the bar is commonly possible with a LBBS compared to a HBBS... though this may differ for someone who practices the HBBS more often. (I'll also comment that a "standard" or "perfect" LBBS is a rare thing to see, though I think the SS coaches are really good at coaching their method.)
During a squat, the hamstrings do not contract as hard as they could in a hamstring dominant exercise. Why is this so? Biomechanics. The short version is that the hamstrings are antagonists to the quads. Normally, if two opposing muscle groups contract at the same time, the joint would not be able to move at all. Yet the quads and hamstrings
can contract at the same time and the knee can still extend. Why is this so? (This is Lombard’s Paradox.) Because the hamstrings are biarticulate, meaning they they cross both the hip and knee joints. As you squat down, the hamstring must lengthen to allow hip flexion, but shorten to allow knee flexion. The net result is little change in the length – that is, little contraction – of the hamstrings. Little contraction translates to little force production. The hamstrings function only as
dynamic stabilizers, not prime movers, in any type of squat (except perhaps the box squat). If you're doing the LBBS hoping to get a great hamstring workout, you're doing the wrong exercise.
I don't know if you're wrong here, but I'll say my impression is different. And I'm actually very curious to know whether the hamstrings are getting "worked" when they are simultaneously shrotening with a flexing knee and lengthening with the flexing hip in the descent; and then the reverse coming back up: lengthening with an extending knee and shortening with an extended hip. SS says they are being heavily worked (and therefore strengthened) through isometric contraction.
(Edited) I believe my hamstrings are a lot stronger since I've been LBBS squatting heavier... and I'm quite sure I haven't been doing any hamstring isolation exercises.
As for a front squat, the hamstrings are already shortened in the bottom position, and the muscle can't contract as hard if it's already short, so the glutes have to do most of the work to extend the hip. Logical? Seems so to me.
There's also the matter of the external hip rotators. In the SS LBBS, the knees are shoved out hard as you bend over. This accomplishes a few things - reducing any impingement in the front of the hip, but also getting more muscles involved in the movement (the ones holding your knees out -- abductors and external rotators) and providing a stretch reflex in the adductors which aids in coming back up. More muscles, more weight to move, more strength building opportunity. This also introduces another dimension to the squat, so it's not just a matter of the differences when viewed from the side between a FS, HBBS, LBBS -- it's also what is going on laterally.
As for weightlifters' training... the SS argument isn't that they should do it as part of their training routinely, but rather that they should do it to substantially increase their strength before they become competitive, and/or in the off season. If this is true (and I may be misrepresenting, but that was my impression), then the fatigue or training resources aspects are irrelevant, because you wouldn't be mixing this "getting strong" activity with the skill of weightlifting.
Tension is created by the amount of torque the muscles must produce– more torque means more tension.
Minor item on terminology -- Torque is the force on the joint resulting from moment force, is it not? I'm just confused by the description of the muscles producing torque... Muscles just pull on levers (bones), producing the moment force or torque on the joint that connects them.
Good discussion, and thanks for sharing some of your article excerpts,
@MikeTheBear.