Anticipatory postural control emerges from a predictive and optimized strategy for movement preparation

Humans shift their center of mass (COM) forward before predictable backward floor tilts. This anticipatory movement is accompanied by selective activation of the gastrocnemius muscle (GC), which produces backward torque at the ankle even as the body moves forward. The control mechanism underlying this coordination between forward COM motion and GC activation remains unclear. Here we investigate whether such behavior can be explained within a predictive optimal control framework. In experiments with auditory cues, anticipatory COM shift and GC activation were observed, representing a use of a backward-acting muscle during forward movement. We then developed a musculoskeletal simulation model governed by model predictive control (MPC), which reproduced these patterns. The simulation suggests the body shifts forward by leveraging gravity, while GC activation stabilizes the ankle and prevents collapse. These findings indicate that anticipatory postural responses may result from optimizing predicted future states using internal models that incorporate gravitational dynamics for efficient motor preparation.