Also among the misperceptions that I hear out there about the rectus abdominis, and upper vs. lower abdominals, is that you’ve got to work the rectus throughout its range of motion. Again these might be muscle physiologists speaking but not people who are cognizant of spinal mechanics. For example, when you look at the architecture of the rectus, it’s a muscle with four heads, four contractile components each separated by a lateral tendon.
If it was a muscle designed to work through its full range of motion it would be one long continuous muscle—but it’s not. It anchors the obliques and transmits the hoop stresses laterally through those lateral tendons. If it wasn’t beaded, the oblique forces would rip it apart laterally. In many elite performances the abdominals contract isometrically. Too many bad backs are created by misinformed people thinking they need to train the rectus with repeated full flexion exercises. There are much better and safer ways to do this.
So again if we’re training athletes to perform, the question is do they need to work the lumbar spine through a full range of motion? Lumbar flexibility often increases the risk of future chronicity! For example, I’ve worked with some very good discus throwers and you’d think that discus throwing would require a huge amount of twist in someone’s back. In fact, if you take the twist out of the training, stabilize and lock the ribcage onto the pelvis, and twist through the legs and shoulders, you may actually enhance performance. Certainly it may be required to reduce back symptoms.
Other performance requirements include variables like speed, agility and/or strength for example; all three of these things require stability, perhaps keeping a line of drive down the torso and through the feet into the ground, etc. A stiffened core may be optimal. So, of course this whole issue depends on the person and the task. But in many cases from both performance and safety perspectives, it’s a bit of a myth that the spine needs to be trained through its range of motion.