Thank you for this, Steve Hill.
I never appreciated the mechanism for increased bone density resulting from barbell training as being from your own muscles pulling harder and therefore placing your bones in higher compression. I always thought a heavy bar meant more stress on the bones just... somehow.
As a lowly Chem Eng, perhaps I could be enlightened a bit more concerning the last slide showing torque about the hip joint in terms of mechanics. It's shown that the low bar squat places the most torque about the hip for the same weight, therefore you might conclude that less weight would be theoretically lifted as you reach a limit with a lower mass on the lifter's back. But for completeness, the same calculation about the knee joint would also show the inverse trend in torque about it (the knee), correct? Therefore more can in actual fact be lifted with low bar because why? Because the muscle groups that control hip extension are bigger/stronger than those controlling knee extension? Therefore you would simply rather shift the torque to that joint for better leverage (leverage may be the wrong word here)?