Point force vs Body force in external load for inverse dynamics

[Jeonghwan Jay Lee]

Hello all,

I was struggling with the feasibility of using inverse dynamics tool without center of pressure (COP). As far as I know, inverse dynamics can be done without COP of ground reaction forces by Body Force setup in external loads configuration. I tested it with my experiment data but the results showed a big diffrence compared to the one with using Point Force. To be specific, there are following visible huge difference:

1) Large differeces in magnitude of joint mement
- For instance, the peak hip flexion moments by using Body Force are more than doubled (approx. 100Nm compared to 35Nm from Point Force setup).
2) Reverse moment pattern in angle dorsi plantar flexion moment
- I observed reverse ankle angle moment. The attached image is my result of approx. single gait cycle (Heel strike to toe off). Vertical dashed line is about the timing of push-off. Point kinematics results showed the negative sign which means dorsi plantar flexion.

Does anyone have the similar issue with mine? I am not convinced which method I should use to get better joint moment outcomes.

Thank you for the help in advance!

Best
Jay