Investigating the effects of spring-loaded knee brace stiffness on gait biomechanics through predictive simulation

This study aims to elucidate the biomechanical effects of varying spring‐loaded knee brace (SLKB) stiffness on knee joint mechanics. This study combined musculoskeletal modeling with a direct collocation optimal control framework to perform a predictive simulation of walking under varied SLKB stiffness (0–1.0 Nm/deg), walking speeds (1.1–1.5 m/s), and slopes (level, 5°/10° uphill and downhill). A multi‐term cost function minimized metabolic energy, muscle activation rates, actuator excitations, joint accelerations, and joint‐limit penalties, yielding physiologically realistic trajectories that satisfied dynamic, path, and boundary constraints. Low‐stiffness SLKBs closely matched the no‐brace baseline, whereas increasing stiffness progressively restricted knee range of motion, induced minimal ground reaction force changes except under incline conditions, elevated knee flexor activations (biceps femoris, lateral gastrocnemius) for foot clearance, and reduced vastus medialis activity during inclined and declined walking. Crucially, medium to high‐stiffness SLKBs produced consistent early‐stance unloading of the knee vertical joint reaction force—up to 29.3% reduction uphill and 23.6% reduction downhill—although unloading effects attenuated or reversed in mid‐ and late‐stance. Increasing SLKB stiffness influenced knee kinematics and muscle activations, with phase‑ and condition‑dependent unloading effects, particularly during uphill walking. These findings suggest potential benefits for knee osteoarthritis, warranting in vivo validation and the development of subject‐specific, condition‑adaptive designs.