Foot pressure measurements should be comparable – with respect to the same subject, between left and right, but also across larger subject cohorts with different shoe sizes.
The physical plantar pressure, given in N/cm², of course depends on the weight of the wearer. Heavier subjects will generally result in higher pressure values, so we may want to normalize the foot pressure by the body weight, or analyze the pressure distribution in relative terms (as e.g. the center of pressure (COP) does).
Apart from the weight aspect, however, we want to be able to compare pressure distributions directly, and run numerical analyses of e.g. large-scale measurement campaigns without any need for subject-specific data modifications.
Foot pressure sensing with scaling sensor geometries
The OpenGo Sensor Insoles ensure a comparable foot pressure sensing across different shoe sizes by perfectly scaling sensor geometries:
- The left and right sensor layouts are exactly symmetric.
- With different sizes, the sensors scale in the same way as the sensor insole outlines, including the sensor areas and centers.
- This way, each foot pressure sensor always covers the same physiological foot area. Note that this would be different if the sensor insole had a matrix of equal-size sensors, with varying number of such sensors depending on the shoe size.
Coordinate system considerations
The OpenGo Sensor Insoles scale faster in length than in width, which is simply what the human foot does. Larger sizes are therefore more “stretched” than smaller sizes. This affects the sensor insole outline and, as described above, the foot pressure sensor locations. This, in turn, has an impact on center of pressure (COP) calculations, for which the sensor locations matter.
Don’t worry. With OpenGo, all COP data is given in a size and side agnostic, normalized coordinate system. This way, you can carry out e.g. gait analysis studies comparing the gait line length of different subjects with varying shoe sizes. It allows you to directly compare the normalized gait line lengths without considering subject meta information about the respective sensor insole size.
The COP data is not normalized in the OpenGo Software, but already normalized and transmitted by the OpenGo Sensor Insole itself. Consequently, the same normalized COP data is available when using OpenGo SDKs and APIs for customized foot pressure analyses.
