Probability of valid gait data acquisition using currently available force plates.

A major difficulty in using force plates for gait analysis is to have a foot fall completely on the instrument while not having the other foot in contact with the same device. This translates into more trials (and time) required to obtain valid data. In order to estimate the probability of a successful trial, which is related to the overall number of trials required, the dimensional relationships between force plate, foot and gait cycle were investigated. In particular, it was analyzed how the dimensions of the plate, the size of foot, the step length and width affect the probability of having a successful trial when acquiring one or two subsequent foot falls using one or two force plates respectively. The equations obtained can also be used to estimate the force plate dimensions that allow for the minimum number of trials for a specific group of subjects. To illustrate this approach, commercially available force plate sizes were statistically evaluated using gait data collected in recent years at The Ohio State University Gait Laboratory from patients with different pathologies. The force plate length maximizing the probability of a successful trial was identified for this specific population.