The force the ground pushes back with when you move on it.
Ground reaction force is the force the ground exerts back on the body, equal and opposite to the force the body exerts into the ground, per Newton's third law. A force plate captures this as three components — vertical, anterior-posterior (braking/propulsion), and medio-lateral — usually expressed relative to body weight and tracked across the stance or contact phase.
GRF data gives an objective read on how load is being absorbed and produced, which underpins conversations about return-to-sport readiness, limb symmetry, and rehab progression after lower-limb injury. It's particularly useful for flagging landing strategies or braking patterns that may be linked to elevated injury risk, such as ACL reinjury, so decisions aren't based on visual impression alone.
Typically measured via a force plate embedded in the floor or a portable platform, during tasks like drop landings, countermovement jumps, sprinting, or cutting manoeuvres. Clinicians look at peak vertical force, loading rate, time to peak force, and left-right asymmetry indices, often alongside video or motion capture to contextualise the movement strategy producing the force trace.
Force plates are not available in most clinical settings, so findings from lab-based GRF testing don't always translate to gym-floor decision-making without cheaper proxy measures. GRF magnitude alone doesn't explain why a pattern is occurring — it needs to be interpreted alongside joint kinematics and kinetics, and single-session data can be affected by task familiarity, fatigue, or fear of movement rather than true capacity.
This guide was auto-drafted and is pending editorial review.