Understanding ground reaction force (GRF) gives insight into external loads experienced by the body. Force platforms are usually required to measure GRF, limiting the understanding of external loads and player-surface interaction in field sports. This is a key consideration for boot and turf manufacturers. This project developed a portable, inertial measurement unit based system to estimate GRF in field-based settings.
The challenge
Characterising ground reaction force, to understand the shoe-surface interaction, is critical to the understanding of football player movement. However, force platforms - the gold standard for measuring ground reaction force - are expensive and typically cannot be installed underneath artificial, hybrid or natural turf surfaces. Moreover, the distinct size of force platforms limits the ability to understand the shoe-surface interface, across a wide-range of movements.
Therefore, a novel method, using inertial measurement units (IMUs) to estimate ground reaction force, was developed.
The method
Eight IMUs were attached to the feet, shanks, thighs, pelvis and trunk. IMU acceleration data were transformed into a global coordinate system and ground reaction force components (e.g. vertical and medio-lateral) were estimated using a Newtonian mechanics model, based on Zatsiorsky-Seluyanov's body segment inertia parameters. A simple lateral bounding task, which requires a player to exert high vertical and medio-lateral loads, was used to compare the IMU-based estimate to force platform data.
The impact
Previous IMU-based ground reaction force results had only considered vertical force components. The current method considered vertical and medio-lateral force components, and estimates were to a high accuracy than previously reported. The current method therefore allows for the assessment of ground reaction force for dynamic, football-based movements in field-based settings.
The method has already been applied to during an assessment of football surface and boot type, and highlighted boot-related effects during acceleration phases in an agility course.
