Relationship Between Vertical Ground Reaction Force and Acceleration from Wearable Inertial Measurement Units During Single-Leg Drop Landing After Anterior Cruciate Ligament Reconstruction

The purpose of this study was to clarify the relationship between vertical ground reaction force (VGRF) and acceleration from wearable inertial measurement units (IMUs) during single-leg drop landing after anterior cruciate ligament reconstruction (ACLR). Twenty-six participants, 42.4 ± 5.3 weeks after ACLR, performed three single-leg drop landing trials bilaterally. The peak VGRF was assessed using a force plate. The resultant acceleration was calculated using IMUs attached to the shank, thigh, and lumbar region. Univariate regression analysis was performed to examine the linear relationship between the VGRF and resultant acceleration. The limb symmetry index (LSI) of the VGRF was linearly associated with the LSI of the resultant accelerations at the shank, thigh, and lumbar sensors (R2 = 0.166, p = 0.039; R2 = 0.525, p < 0.001; and R2 = 0.250, p = 0.009, respectively). In the involved limb, only the resultant acceleration at the thigh was a significant predictor of VGRF (R2 = 0.490, p < 0.001), whereas in the uninvolved limb, the resultant accelerations at the shank, thigh, and lumbar sensors were significant predictors of VGRF (R2 = 0.245, p = 0.010; R2 = 0.684, p < 0.001; and R2 = 0.412, p < 0.001, respectively). Caution may be required when using IMUs to predict VGRF asymmetry because the coefficient of determination for predicting VGRF is lower in the involved limb than in the uninvolved limb.