Composite Poisson’s Ratio as a Candidate Measure of Pelvic Floor Functional Reserve: A Testable Hypothesis Based on Bladder–Levator Plate Force–Deformation Coupling

Current clinical assessment of female pelvic floor function is dominated by anatomical staging and voluntary muscle-strength testing. These measures are clinically useful but do not directly quantify how the pelvic floor responds as a coupled mechanical system during transient increases in intra-abdominal pressure. We propose a third, complementary dimension—functional reserve—and introduce the Composite Poisson’s Ratio (Vc) as a candidate dimensionless response index for this purpose. Vc is defined as the ratio between the relative change in effective bladder–levator plate contact area and the relative craniocaudal displacement of the bladder neck during a standardized loading maneuver. The concept is inspired by the near-incompressible behavior of hydrated soft tissues and by the possibility that deformation can increase apposition and redistribute load across pelvic support interfaces. Importantly, Vc is not claimed to be a classical material Poisson ratio or an intrinsic tissue constant; it is a system-level, geometry- and boundary-condition-dependent metric that remains to be validated. The hypothesis predicts that mechanically stable pelvic floors will show reproducible coupling between organ displacement and contact-area adaptation, whereas reduced or disorganized coupling will be associated with greater relative displacement and pelvic floor dysfunction. We outline a staged validation program using dynamic imaging, tissue mechanics, contact-aware computational modeling, and prospective clinical studies. If Vc is not reproducible, does not distinguish stable from dysfunctional states, or adds no predictive value beyond established measures, the proposed framework should be revised or rejected.