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Decreased force under dorsiflexed foot?

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  • Decreased force under dorsiflexed foot?

    Dear Biomch-L community,
    I am simulating human standing posture using the software Simwise4D for dynamic simulations. The principal anatomical segments are represented as rigid bodies with measures and masses calculated from anthropometric measurements and data from literature.
    Rigid constraints, rotational constraints and springs were used to keep the model in an upright standing position. In particular, from the head to the pelvis, all bodies were linked by means of rigid constraint; hip and knee flexion extension and ankle dorsiflexion plantarflexion were allowed using rotational constraints.
    Spring/damper elements were used to simulate the principal muscles of the lower limbs and for each one elastic coefficient and natural length were set.
    I am measuring the force under each foot by means of two force sensors.
    When I reduce natural length of the spring simulating the tibialis anterior of the left leg, its tension increased and a dorsiflexion was simulated.
    Then, I measure a reduction of force under the left foot and the increment of force under right foot.

    I would like to know if you agree with this behavior of the model or not. What is your physically explanation or interpretation of the reduction of the force under the stimulated foot?

    Thank you so much!

  • #2
    Re: Decreased force under dorsiflexed foot?

    During dorsiflexion, the heel moves downward relative to the ankle. So the right leg effectively gets longer and this may cause your model to start leaning to the left. With the body center of mass more above the left foot, the force under the left foot would increase.

    To see if this explanation is correct, check if the posture has changed in the way I describe.


    Ton van den Bogert


    • #3
      Re: Decreased force under dorsiflexed foot?

      Depending on how your model is set up, pressure rather than force might also be a factor. By dorsiflexing the foot there is less contact area to distribute downward force over, this reduction in surface/contact area will therefore result in greater pressure over the remaining contact areas.

      This is particularly important if the foot size is greater than the surface area of the force sensor, as some load would not have been accounted for.