Linear dependence of peak, mean, and pressure-time integral values in plantar pressure images

Dynamic plantar pressure images are routinely used in clinical gait assessment, and peak pressure, mean pressure, and pressure-time integral are the most frequently used parameters to summarize these images. Many studies report only one parameter, but other studies report all three. The interdependency of these variables has not been explicitly studied previously. The purpose of this study was to describe the linear relation between these three pressure parameters. 327 subjects walked normally over a pressure plate. Peak pressure, mean pressure and pressure-time integral were calculated for 10 different anatomical areas and, after applying a previously described spatial normalization procedure, these variables were also calculated for each pixel. Mean pressure was highly correlated with peak pressure (r=0.90+/-0.09) and pressure-time integral (r=0.81+/-0.13) for pixels. Peak pressure and pressure-time integral showed a linear correlation coefficient of r=0.78+/-0.21. The pressure parameters of the forefoot pixels were more highly correlated than the heel pixels. The current results have two major implications: (1) plantar pressure parameters (peak, mean, and impulse) can be reasonably compared across studies, even across parameters, and (2) the variables most commonly used to characterize plantar pressures are highly inter-correlated, implying that a smaller set of parameters may more efficiently capture the biomechanical behavior of interest.