I haven't read their stuff, all the information I've ever read including stuff from Dr.Hatfield indicated it did, here are a couple things:
http://www.physicaltherapist.com/articles/view/id/3
Increased stress on the patellar tendon as the knees go past the toes. There are times in life and in the weight room where the knee will make its way out past the toes, especially with squats and lunges. If the heels are down and hips are contributing properly then no problem. Once the heels come off the floor you can kiss any glute contribution good-bye. It's all quad from there on out which means greater stress on the patellar tendon, shearing forces, and those nasty compressive forces again as well.
http://www.bodybuilding.com/fun/drsquat12.htm
http://www.bodybuilding.com/fun/drsquat12.htm
During the descent phase of any type of squat, do not allow the knees to extend beyond your feet. The further your knees travel over your feet, the greater the shearing forces on the patellar tendon and ligament.
But who knows, maybe they are wrong.
I read an article a long, long, long time ago that showed the value of the shearing forces on the patellar tendon in those different positions and it was markedly higher on them in that position. But I'd have to agree with one thing that perhaps this idea got started because people who usually have their knees out past their toes can sometimes come up off their heels and lean forward...maybe that is where this whole idea was generated.
Glad you posted that, I haven't looked into this stuff for a long time.
http://www.exrx.net/Kinesiology/Squats.html
