Breathing Is the Switch for Trunk Stiffness: Intra-Abdominal Pressure as a Throttle (The Kuriyama Protocol, Chapter 7)

Part 12 of a series; the seventh of fifteen chapter-by-chapter articles. Part 1: 10.5281/zenodo.23587879 · Part 2: 10.5281/zenodo.23587670 · Part 3 (v2): 10.5281/zenodo.23723510 · 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 · Part 10: 10.5281/zenodo.23686289 · Part 11: 10.5281/zenodo.23720048 Chapter 7 of The Kuriyama Protocol treats breathing as the controller of trunk stiffness Π₃ = P L² / (m g). Breathing is the most repeated movement (about 22,000 breaths per day). The trunk core is a pressure vessel (diaphragm, pelvic floor, transversus abdominis, multifidus), not a single muscle. Raising intra-abdominal pressure stiffens the trunk and reduces rotation and flexion range, so stiffness and range trade off and optimal pressure is a function of task and phase. "Always exhale during exercise" fixes the trade-off; the claim is "remove always", not "do not exhale", with blood-pressure safety as a legitimate change of objective. Hyperlordosis is redefined functionally as inability to exhale and close the ribs. Abdominal muscles switch on under three conditions (push, exhale, flex) rather than by instruction. Four gaps found while writing, not stated in the book: - The claim that habit strength is set by repetition count, so training cannot override 22,000 daily breaths, contradicts Part 4's update rule (no repetition term). Reconciled: use-dependent learning entrenches the pattern, but rewriting depends on gated error. - "200×" compared a daily count with a weekly one (weekly ratio is about 1,500×), and "the causal direction is clear" overstated a closed loop in which rib-cage configuration also constrains breathing. - The breath-hold versus exhale comparison confounded intra-abdominal pressure with lung volume. - An overstatement corrected for Chapter 4 in Part 9 remained in Chapter 7; a book-wide search found and corrected four further unpropagated passages. Five falsifiable predictions are registered (numbered 52–56, continuing the series): - P52. With equal repetitions, exhalation retraining with tactile error feedback yields greater next-day improvement than verbal cueing. - P53. Seated trunk rotation range depends mainly on abdominal bracing, not lung volume (2 × 2 design). - P54. Breathing with ribs held closed reduces lumbar lordosis more, and more durably, than the cue "round your lower back". - P55. Push–exhale–flex conditions produce greater deep abdominal and lower erector spinae activity than "tighten your abdomen". - P56. Smaller lower-rib circumference excursion predicts smaller seated trunk rotation range. Refutations are welcome. 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: contact@medi-gym-revital.com