Don’t rotate at the lumbar spine? I think coaches should think about not trying to force motion at locations instead of staying in the land of isometric safety. In sprinting the best performances had matching rotation actions based on the frequency of touch down and phase of the race. Very little axial rotation int the acceleration, but at top speed the arms did rotate as well as swing back and forth. If we did more core training would that fix the problem? No. The best sprinters in the world as well as the best at executing what they have keep the shoulders squared and steady. As they rise they shoulders allow for whatever english happens from the forces below and they harness it, not fight the rotation. Relaxation is about contrasting the brute power of intent while learning to turn off unnecessary contractions. Teaching it is very individual and the holy grail in sprinting.