Where Is the Power Source? The Spine Engine Revisited (The Kuriyama Protocol, Chapter 5)

Part 10 of a series; the fifth of fifteen chapter-by-chapter articles. Part 1: 10.5281/zenodo.23587879 · Part 2: 10.5281/zenodo.23587670 · Part 3: 10.5281/zenodo.23526074 · Part 4: 10.5281/zenodo.23609857 · Part 5: 10.5281/zenodo.23610607 · Part 6: 10.5281/zenodo.23682055 · Part 7: 10.5281/zenodo.23684537 · Part 8: 10.5281/zenodo.23684996 · Part 9: 10.5281/zenodo.23685960 Chapter 5 of The Kuriyama Protocol claims that the limbs are wheels and the spine is the engine. This article checks that claim and narrows it. In end-point-speed tasks (throwing, striking, swinging) it matches the proximal-to-distal sequence. In locomotion it does not: the ankle performs roughly 40% of positive joint work in fast walking and running (Farris & Sawicki, 2012). Ten sections are covered: the contact condition as a boundary condition that turns the same body into different machines; force ascending while coordinates descend, meeting at the spine; hips close-packed (internal rotation) to push and loose-packed (external rotation) to receive, alternating in gait; the pelvis as a crank driven by a force couple (torque = F × d, net force 0); oblique trunk slings that store and return energy; alternating mobile and stable joints as a default allocation; open versus closed kinetic chain as a continuum, indexed as external resistance / applied force; triple extension and preceding absorption; upward propagation of collapse. Three gaps found while writing, not stated in the book: - "Limbs only transmit" was generalized from end-point-speed tasks without stating that scope. - "One support axis gives the deepest rotation" does not hold numerically, since one-directional pelvic rotation is limited to about 45° by hip range in both single and double stance; the effect is reinterpreted as greater pelvis–thorax counter-rotation. Airborne reorientation also does not require limb counter-rotation (falling-cat mechanism). - The field cue "extend hip, knee and ankle simultaneously" conflicts with the proximal-to-distal sequence in vertical jumping (Bobbert & van Ingen Schenau, 1988); alignment marks the end of push-off, not its peak. Five falsifiable predictions are registered (numbered 44–48, continuing the series): - P44. In throwing, "rotate the spine, let the arm hang" yields higher ball speed and lower forearm EMG than "swing the arm fast". - P45. Pelvis–thorax relative twist is largest in single-leg stance, while differences in thorax rotation in space are smaller. - P46. Holding hip external rotation during push-off delays force development; holding internal rotation during landing increases knee valgus. - P47. Trunk EMG shows a person-specific breakpoint as pushing resistance increases. - P48. Cueing simultaneous triple extension does not raise, and may lower, jump height. If it holds, the field cue should be revised. Refutations are welcome, especially on P48. The author has no formal research training. Corrections will be issued as new versions, with earlier versions kept retrievable. The article body is in Japanese. An English summary, the registered predictions and the reference list are included in the document. Contact: [email protected]