Ambulatory ground reaction forces with quasi-piezoelectric nanocomposite foam

Accurate measurement of 3D ground reaction force (GRF) that is transmitted to the human musculoskeletal system during walking and running can help to increase our understanding of certain musculoskeletal pathologies and athletic performance. However, to date accurate GRF measurements have only been obtained in a laboratory, using expensive instruments (e.g., force platforms). In recent work, our laboratory has developed a quasi-piezoelectric, nanocomposite foam; when placed in a shoe sole, this novel "smart foam" can be used to measure GRF under a broad range of real world conditions, outside of the laboratory. This paper describes the results of a study that was designed to evaluate the accuracy of GRF measurements using "smart foam" sensors during walking and running for subjects of varying body mass. While wearing the smart shoe, subjects ambulated on a treadmill that was instrumented with a force platform at various walking and running speeds. We then used (1) preferred-speed walking GRF, measured via the instrumented treadmill, and (2) voltages that were created from the "smart foam", to create a statistical model. Separate models were created for each trial from a range of random foot strikes. This model was then used to estimate 3D GRF during the remainder of the walking and running trials. By comparing the measured (treadmill) and estimated (statistical model) GRF, the ability of the "smart foam" to estimate walking and running GRF was quantitatively evaluated.