Abstract
Ground reaction forces and moments (GRF&M) are important measures used as input in biomechanical analysis to estimate joint kinetics, which often are used to infer information for many musculoskeletal diseases. Their assessment is conventionally achieved using laboratory-based equipment that cannot be applied in daily life monitoring. In this study, we propose a method to predict GRF&M during walking, using exclusively kinematic information from fully-ambulatory inertial motion capture (IMC). From the equations of motion, we derive the total external forces and moments. Then, we solve the indeterminacy problem during double stance using a distribution algorithm based on a smooth transition assumption. The agreement between the IMC-predicted and reference GRF&M was categorized over normal walking speed as excellent for the vertical (ρ = 0.992, rRMSE = 5.3%), anterior (ρ = 0.965, rRMSE = 9.4%) and sagittal (ρ = 0.933, rRMSE = 12.4%) GRF&M components and as strong for the lateral (ρ = 0.862, rRMSE = 13.1%), frontal (ρ = 0.710, rRMSE = 29.6%), and transverse GRF&M (ρ = 0.826, rRMSE = 18.2%). Sensitivity analysis was performed on the effect of the cut-off frequency used in the filtering of the input kinematics, as well as the threshold velocities for the gait event detection algorithm. This study was the first to use only inertial motion capture to estimate 3D GRF&M during gait, providing comparable accuracy with optical motion capture prediction. This approach enables applications that require estimation of the kinetics during walking outside the gait laboratory.
Highlights
Assessment of ground reaction forces and moments (GRF&M) is an important stage in the biomechanical analysis procedure
Small differences were found in the anterior GRF where optical motion capture (OMC) provided higher accuracy (OMC: rRMSE = 7.4%, inertial motion capture (IMC): rRMSE = 9.4%)
Compared to the dynamic contact model developed by Fluit et al [16], we found similar correlation coefficients in all components, apart from the transverse plane, which was much higher in our case (IMC: ρ = 0.826; OMC: ρ = 0.825; Fluit et al.: ρ = 0.704)
Summary
Assessment of ground reaction forces and moments (GRF&M) is an important stage in the biomechanical analysis procedure. The fixed position of the plates on the ground together with the requirement to step with the whole foot on the plate for a successful measurement may cause subjects to alter their natural gait pattern Due to their high cost, most laboratories are equipped with one or a couple of FPs, which makes tracking many successive steps during overground walking impossible. The main difference between these two systems is that the former measures only a pressure distribution in the shoe, whereas the latter measures directly three-dimensional forces applied beneath the shoe Such devices have enabled ambulatory estimation of ankle kinetics [7] and knee kinetics [8], in combination with inertial measurement units (IMUs) and linked segment models. As for the instrumented force shoe, it has been suggested that optimization is needed to decrease the size and weight of its wearable instrumentation and make it practical for recording sessions of extended durations [11,12]
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