Implementing an accelerometer-based pelvis segment for low back kinetic analyses during dynamic movement tasks.

Area of Science:

• Biomechanics
• Kinesiology
• Ergonomics

Background:

• Accelerometer-based pelvis tracking is used for kinematics but its low back kinetic accuracy is unknown.
• Assessing low back joint reaction moments and contact forces is crucial for injury risk evaluation.

Purpose of the Study:

• To compare L5S1 joint reaction moments and contact forces derived from an accelerometer-based pelvis versus an optically tracked pelvis.
• To introduce and validate an approach for correcting global pelvis position using thigh angle.

Main Methods:

• One participant performed four dynamic tasks (forward bend, squat, sit-to-stand-to-sit, forward lunge).
• A bottom-up inverse dynamics approach was used.
• Root mean square error (RMSE) and coefficient of determination (R² ) quantified differences between optical and accelerometer methods.

Main Results:

• L5S1 reaction flexion-extension moments showed RMSE from 1.32-2.20 Nm (R² ≥ 0.98).
• Net shear and compression forces had RMSEs of 2.13-10.45 N and 0.63-4.96 N.
• L5S1 joint contact forces had RMSEs of 13.45-19.51 N (shear) and 31.18-55.97 N (compression) (R² ≥ 0.85).

Conclusions:

• The accelerometer-based pelvis, with thigh-angle correction, is feasible for computing low back kinetics.
• The calculated errors in joint contact forces are <5% of NIOSH limits, unlikely to affect injury risk interpretation.