I seldom comment on internet comments, but I'll just ask you to think about the role of isometric contraction of abs, erectors, and everything else in a squat or pull. Not every muscle contraction results in a change in muscle belly length. I thought this was commonly-possessed understanding -- agonist/antagonist function, a balance of extension and contraction, etc. This type of thinking is typical of "physios" who only consider the isolated contractile function of individual muscles. What are your comments?