Improved agreement of foot segmental power and rate of energy change during gait: inclusion of distal power terms and use of three-dimensional models.

Traditional models used to calculate foot segmental power have yielded poor agreement between foot power and the rate of energy change during the stance phase of gait and limited the applicability of foot segmental power analyses to swing phase only. The purpose of this study was to improve the agreement of foot segmental power and rate of energy change by using more inclusive models to calculate foot segmental power and energy. The gait of 15 adult subjects was studied and models were used to calculate foot segmental power that included either the proximal terms only (Model P, the most common method in the literature) or both proximal and distal terms (Model PD, a mathematically complete model). Power and energy terms were computed in two ways, from sagittal plane vector components only (two-dimensional condition) and from complete three-dimensional components (three-dimensional condition). Results revealed that the more inclusive the model, the higher the agreement of foot power and rate of energy change. During stance phase, Model P produced poor agreement (r(c) = 0.108) for both two-dimensional and three-dimensional conditions, Model PD-2D yielded higher agreement (r(c) = 0.645), and Model PD-3D exhibited nearly perfect agreement (r(c) = 0.956). The advantages of a segmental power analysis include the ability to identify the mechanisms of energy transfer into and out of the foot during movement. The results of this study suggest that foot power analyses are valid when using Model PD-3D to describe foot function during locomotion.