I think these exercises are used to teach “anti-rotation” of the lumbar spine a la Stuart McGill’s approach where a neutral spine is emphasized with good hip mobility. I actually think this approach makes some sense; even though I know it flies in the face of the Charlie Francis system where hip and spine mobility are emphasized in the core/abdominal movements.
Couldn’t this type of stabilization exercises be a valuable exercise for a novice runner/athlete who over “rotates” when sprinting?
Also, since the spine loads are less in the plank/bridge exercises they may be a bit safer than taking the lumbar spine through flexion and flexion/rotation combination exercises which are challenging to the intervertebral discs. Comments, opinions??