Consumer-priced wearable sensors combined with deep learning can be used to accurately predict ground reaction forces during various treadmill running conditions

Ground reaction force (GRF) data is often collected for the biomechanical analysis of running, due to the performance and injury risk insights that GRF analysis can provide. Traditional methods typically limit GRF collection to controlled lab environments, recent studies have looked to combine the ease of use of wearable sensors with the statistical power of machine learning to estimate continuous GRF data outside of these restrictions. Before such systems can be deployed with confidence outside of the lab they must be shown to be a valid and accurate tool for a wide range of users. The aim of this study was to evaluate how accurately a consumer-priced sensor system could estimate GRFs whilst a heterogeneous group of runners completed a treadmill protocol with three different personalised running speeds and three gradients. Fifty runners (25 female, 25 male) wearing pressure insoles made up of 16 resistive sensors and an inertial measurement unit ran at various speeds and gradients on an instrumented treadmill. A long short term memory (LSTM) neural network was trained to estimate both vertical <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo> <mml:mi>G</mml:mi> <mml:mi>R</mml:mi> <mml:msub><mml:mi>F</mml:mi> <mml:mi>v</mml:mi></mml:msub> <mml:mo>)</mml:mo></mml:math> and anteroposterior <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo> <mml:mi>G</mml:mi> <mml:mi>R</mml:mi> <mml:msub><mml:mi>F</mml:mi> <mml:mrow><mml:mi>a</mml:mi> <mml:mi>p</mml:mi></mml:mrow> </mml:msub> <mml:mo>)</mml:mo></mml:math> force traces using leave one subject out validation. The average relative root mean squared error (rRMSE) was 3.2% and 3.1%, respectively. The mean <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo> <mml:mi>G</mml:mi> <mml:mi>R</mml:mi> <mml:msub><mml:mi>F</mml:mi> <mml:mi>v</mml:mi></mml:msub> <mml:mo>)</mml:mo></mml:math> rRMSE across the evaluated participants ranged from 0.8% to 8.8% and from 1.3% to 17.3% in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo> <mml:mi>G</mml:mi> <mml:mi>R</mml:mi> <mml:msub><mml:mi>F</mml:mi> <mml:mrow><mml:mi>a</mml:mi> <mml:mi>p</mml:mi></mml:mrow> </mml:msub> <mml:mo>)</mml:mo></mml:math> estimation. The findings from this study suggest that current consumer-priced sensors could be used to accurately estimate two-dimensional GRFs for a wide range of runners at a variety of running intensities. The estimated kinetics could be used to provide runners with individualised feedback as well as form the basis of data collection for running injury risk factor studies on a much larger scale than is currently possible with lab based methods.