> the gist of the "wrong" is that we've been trained by "trainers" (over-padded athletic shoes) to run in a straight-legged, heel-lands-first manner. When you do that, your knee is locked (or at least straight) as the foot lands, which transmits the force of the landing up your leg and into your lower back.

Any of a sufficiently competent teacher, sufficient miles, or sufficient speed will train you not to do that.