Background: Power and energy at the ankle joint during gait are usually computed considering the foot as a rigid body. The foot is instead a deformable structure and can absorb and produce energy by pronation/supination, foot arch deformation and other intrinsic movements.Research question: Is it feasible to improve the foot power and energy estimation during gait with a simple gait analysis protocol?Materials and Methods: The power exchanged between the foot and the shank was computed as the sum of rotational and translational power, intrinsically considering the foot deformation ("Deformable Foot method", DF). By this method the only shank movements and ground reaction forces need to be analysed. Eighteen healthy subjects were evaluated while walking barefoot and shod at different velocities. We then compared the obtained results with those obtained by the conventional power and energy calculation method ("Ankle Joint method", AJ). Results:The DF method showed a consistent negative peak of power absorption during the load acceptance (-1.16±0.47 W/Kg barefoot, -1.08±0.44 W/Kg shod), barely visible with the AJ method (-0.23 ±0.09 W/Kg barefoot, -0.30±0.09 W/Kg shod). The maximum power production calculated with the DF method (2.44±0.56 W/Kg barefoot, 2.49±0.57 W/Kg shod) was significantly lower than to the one calculated with the AJ method (3.15±0.68 W/Kg barefoot, 3.09 ±0.69 W/Kg shod). Similarly, the final energy values, the energy absorbed and produced were different between the two methods.Significance: Neglecting the foot deformations during gait leads to underestimate power absorption and overestimate power production. The DF method does not require a complex gait analysis protocol and can provide important information about the internal structure of the foot, thus improving physiological and clinical assessment.

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