A force plate is a measuring instrument that quantifies the forces and moments generated when a body interacts with a surface. It assesses how individuals produce force, maintain balance, and execute movements, providing objective data on physical performance and biomechanics. These devices are commonly found in medicine, sports, and research.
How Force Plates Capture Data
Force plates function by converting mechanical force into an electrical signal through specialized sensors. Two primary types of sensors are commonly employed: strain gauges and piezoelectric sensors. Strain gauge force plates utilize small electrical resistors that change their resistance when deformed by mechanical strain. When force is applied to the plate, the underlying spring body deforms, causing attached strain gauges to stretch or compress, altering their electrical resistance. This change is measured and converted into a voltage signal proportional to the applied force.
Piezoelectric force plates contain crystals that generate an electrical charge when subjected to mechanical stress. These sensors are exceptionally stiff and measure with minimal deformation, making them suitable for capturing rapid, high-frequency force changes like impacts. The electrical charge produced by the piezoelectric crystals is then captured and transformed into a voltage signal by a charge amplifier.
Key Data Points Measured
Force plates primarily measure ground reaction forces (GRFs), which are the forces exerted by the ground on a body in contact with it. According to Newton’s third law, this is an equal and opposite reaction to the force the body applies to the ground. GRFs are three-dimensional, with vertical, anterior-posterior (forward-backward), and medial-lateral (side-to-side) components. The vertical component counteracts body weight and is significant for supporting mass and analyzing jumps. The anterior-posterior component relates to propulsive or braking forces, influencing acceleration and deceleration. The medial-lateral component affects stability and balance, indicating side-to-side forces.
The Center of Pressure (CoP) is another measurement, representing the point on the supporting surface where the ground reaction force is effectively applied. It is the average location of the pressure distribution under the foot or feet. Analyzing CoP movement provides insights into balance control and postural stability, with shifts indicating adjustments to maintain equilibrium. For instance, during walking, CoP typically moves from the heel towards the toes.
Force plates also measure moments, or torques, which are rotational forces. A moment is the turning effect of a force around an axis of rotation and is calculated from the applied force and its distance from the pivot point. These measurements help understand how rotational forces act on joints during movement. Impulse, the product of force and the time over which it is applied, can also be calculated. Impulse is represented by the area under a force-time curve and indicates the change in momentum, which is particularly relevant in activities like jumping.
Diverse Uses of Force Plate Technology
Force plate technology is applied across various fields to understand human movement and performance. In sports performance, force plates analyze athletic movements like jumping, sprinting, and lifting. This data helps coaches and trainers optimize technique, assess strength and power output, monitor training effectiveness, and identify imbalances, contributing to performance enhancement and injury prevention. For example, jump tests using force plates can measure an athlete’s peak force, rate of force development, and limb asymmetry.
In clinical biomechanics and rehabilitation, force plates assess gait abnormalities, balance disorders, and track recovery progress following injury or surgery. They provide objective data to evaluate how an injury affects a patient’s movement mechanics, detect compensatory patterns, and customize rehabilitation protocols. This allows clinicians to monitor improvements over time and make data-driven decisions regarding treatment plans and return to activity.
Ergonomics uses force plate measurements to analyze workplace movements and design safer environments and equipment. By understanding the forces exerted during tasks, potential risks for work-related injuries can be identified and mitigated.
Force plates are a tool in biomechanics and kinesiology research, enabling scientists to quantify and analyze human movement. Researchers use this technology to understand movement biomechanics, assess the impact of disease or training on movement patterns, and develop interventions to improve movement and reduce injury risk.