Gait Joint Moment Inverse Dynamics Calculator
Human motion analysis & clinical gait mechanics: Compute sagittal plane ankle and knee joint moments ($M_{\text{joint}}$) and Achilles tendon tension from force plate ground reaction forces ($GRF$).
Subject & Force Plate Inputs
Body weight BW = M · 9.81 N
Vertical force (typically 110–125% BW at push-off)
Negative = Propulsion forward (+ = Braking)
Joint Moment Arms (Center of Pressure to Joint)
Horizontal distance from COP to lateral malleolus
Ankle center to Achilles tendon centerline
Inverse Dynamics Moment Formulation
Neglecting foot segment mass and angular acceleration for quasi-static equilibrium:
$$M_{\text{ankle}} = F_z \cdot d_a + F_y \cdot h_a$$
Achilles tendon tension: $F_{\text{Achilles}} = \frac{M_{\text{ankle}}}{r_a}$.
Internal Joint Moments
Ankle Joint Moment (M_ankle)
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Normalized Moment (N·m/kg)
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Muscle & Tendon Forces
Achilles Tendon Force (F_AT)
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Triceps surae muscle tension
Tendon Load (Multiples of BW)
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F_AT / (M · g)
Ground Reaction Vector
Resultant GRF Vector:
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GRF Vector Orientation:
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Gait Biomechanical Status:
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