Table 3.
Joint reaction force (normalized to body weight) comparisons between inertial measurement units and optical motion capture.
| Froude | Axis | L5/S1 | T12/L1 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| RMSE | NRMSE | R | Lag | RMSE | NRMSE | R | Lag | ||
| 0.1 (Walk) | Comp | 0.01 | 0.05 | 1.00 | 0 | 0.06 | 0.32 | 1.00 | 0 |
| AP shear | 0.10 | 1.15 | 1.00 | 0 | < 0.01 | 0.01 | 1.00 | 0 | |
| ML shear | 0.03 | 0.51 | 0.59 | − 10 | < 0.01 | 0.02 | 0.81 | 0 | |
| 0.2 (Walk) | Comp | 0.06 | 0.12 | 1.00 | 0 | 0.08 | 0.22 | 0.99 | 0 |
| AP shear | 0.08 | 0.44 | 1.00 | 0 | < 0.01 | 0.01 | 1.00 | 0 | |
| ML shear | 0.01 | 0.23 | 0.75 | − 3 | < 0.01 | 0.02 | 0.63 | 1 | |
| 0.3 (Walk) | Comp | 0.05 | 0.08 | 0.99 | 0 | 0.07 | 0.14 | 0.98 | 0 |
| AP shear | 0.09 | 0.47 | 1.00 | 0 | < 0.01 | 0.02 | 1.00 | 0 | |
| ML shear | 0.02 | 0.19 | 0.75 | − 12 | < 0.01 | 0.00 | 0.58 | − 4 | |
| 0.6 (Run) | Comp | 0.06 | 0.03 | 1.00 | 0 | 0.14 | 0.11 | 1.00 | 0 |
| AP shear | 0.27 | 0.46 | 0.99 | 0 | 0.01 | 0.26 | 0.85 | 0 | |
| ML shear | 0.08 | 0.74 | 0.61 | − 32 | 0.01 | 0.10 | 0.82 | − 1 | |
| 0.8 (Run) | Comp | 0.12 | 0.06 | 0.99 | 0 | 0.08 | 0.07 | 0.99 | 0 |
| AP shear | 0.30 | 0.53 | 0.99 | 0 | 0.02 | 0.36 | 0.95 | 0 | |
| ML shear | 0.11 | 0.85 | 0.32 | 30 | 0.02 | 0.10 | 0.81 | 0 | |
| 1.0 (Run) | Comp | 0.15 | 0.06 | 0.98 | 0 | 0.25 | 0.15 | 0.98 | − 2 |
| AP shear | 0.25 | 0.30 | 0.99 | 0 | 0.04 | 0.34 | 0.87 | 0 | |
| ML shear | 0.12 | 1.50 | 0.54 | 31 | 0.04 | 0.32 | 0.37 | 19 | |
L5/S1, lumbosacral joint; T12/L1, thoracolumbar joint; Comp, compression; AP, anteroposterior; ML, mediolateral; RMSE, root mean squared error; NRMSE, normalized root mean squared error; R, cross-correlation. Lag is % of stride cycle (positive value indicates OMC signal occurs before IMU signal).