Tibialis Static Lock (TSL™) — Version 1.0: A Dual-Boundary Anchored Isometric Foot Interface for Hemodynamic Support and the Experimental Investigation of Autonomic Coactivation

Tibialis Static Lock (TSL™) — Version 1.0 presents a proposed seated, low-movement physical counter-pressure interface based on a mechanically constrained, dual-boundary foot configuration. In the basic configuration, the heel generates a downward reaction force against a lower boundary while the dorsal forefoot simultaneously generates an upward reaction force against a rigid upper boundary, permitting substantial internal muscular and musculoskeletal loading with minimal visible joint excursion. The work develops the engineering proposition that this dual-boundary anchored isometric configuration may permit controlled recruitment of lower-limb musculature while the user remains seated and externally relatively motionless. It further presents TSL as an experimental platform for investigating whether an intermediate force range may exist in which arterial pressure and/or central hemodynamic support increases while excessive cardiac acceleration is avoided and measurable parasympathetic cardiac modulation remains present. This proposed experimental region is termed the TSL Autonomic Coactivation Window. Version 1.0 distinguishes established physiological principles from TSL-specific hypotheses, defines the proposed mechanical architecture, establishes falsification criteria, and provides a reproducible framework for experimental investigation. No therapeutic efficacy is claimed. TSL is presented as a testable hypothesis and open research platform, not as an established treatment for hypotension, syncope, cardiovascular disease, or autonomic dysfunction. Patent Pending — U.S. Provisional Patent Application No. 64/142,894. Zenodo DOI: 10.5281/zenodo.22140395