Coupling of Pressure Generation and Geometric Transmission: Revised Model Incorporating Mutual Eccentric Contraction and Extensor Latch MechanismCoupling of Pressure Generation and Geometric Transmission: A New Theoretical Framework for Maximizing Ground Reaction Force in Lower Limb Closed-Chain Movement

This paper revises the pressure-generation and geometric-transmission framework proposed in Sato (2026a) by introducing two new mechanisms absent from the original model. First, we demonstrate that the hamstrings and gastrocnemius form a mutual eccentric contraction loop: hamstring contraction elongates the proximal gastrocnemius, while simultaneous gastrocnemius contraction elongates the distal hamstrings. This mutual eccentric contraction maximizes intramuscular pressure in both muscles concurrently via the multi-layer spiral fascial architecture. Second, we propose an extensor latch mechanism analogous to the champagne cork model: extensor muscles at the ankle (tibialis anterior group) and lumbar region (gluteal muscles, erector spinae) act as seals that maintain accumulated pressure, and their active contraction withdraws the latch, triggering explosive pressure discharge. The discharged repulsive force is converted into propulsive ground reaction force exclusively during ground contact; ground departure is the result, not the trigger, of this process. In the vertical stance configuration, force transmission efficiency reaches the theoretical maximum of 100%. This revised framework resolves the SSC energy gap (tendon elastic energy approximately 35 J vs. required jumping energy approximately 300 J) and reframes human takeoff as an active hydraulic system comprising flexor pressurization, extensor sealing, and coordinated latch release.