Golgi Tendon Organ Force Feedback: Inhibition vs. Positive-Feedback Gating

The Golgi tendon organ (GTO) is often introduced as a simple safety switch that inhibits a muscle before it tears — but the reflex circuit it drives is not fixed. This simulator models the same tendon-force sensor feeding a spinal Ib pathway whose sign is switched by the nervous system depending on task: during quiet standing the pathway produces classic autogenic inhibition, while during the stance phase of walking the identical afferent signal is gated into positive force feedback that helps extensor muscles support body weight. A 3D circuit of the sensor, spinal interneuron relay and motoneuron shows spikes travelling the pathway in real time next to a leg model whose tendon tension and force-plate loading respond to the resulting motor drive, with a saturating GTO firing-rate curve that keeps the stance-phase positive-feedback loop stable instead of runaway.