Subtalar Moment Directionality

[JAEHO JANG]

Hi OpenSim Team,

I have a question regarding the directionality of subtalar moments during walking on a treadmill using OpenSim. My understanding is that the joint angles were calculated based on the motion of the proximal segment relative to the distal segment, resulting in plantarflexion being marked as negative (-) and dorsiflexion as positive (+), as shown in the left figure. Where I am confused is in the interpretation of the directionality of the subtalar moment. Is it correct to interpret inversion as negative (-) and eversion as positive (+) on the right side of the figure?

Best,
Jaeho

[Mohammadreza Rezaie]

Hi, it depends on how coordinates are defined in the model you are using. In Rajagopal and gait_2392 models, supination angle is positive and pronation is negative, and internal joint moment [muscles] follows this rule, i.e., supinator moment [+] and pronator moment [-].

[JAEHO JANG]

Thanks so much for your help!