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Vicon Nexus - Generating gait cycle parameters

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  • Vicon Nexus - Generating gait cycle parameters

    Hi

    I am using Vicon plug-in-gait as a means of validating another gait analysis device. I have been unable to find out how the Vicon actually caluculates the gait parameters and specifically how it caluculates distance. I have generated the gait cycle parameters by manually inputing the gait cycle events as I need the calculations to be made over a larger distance than covered by the force plate. The data has been interesting with large discrepency between stance % and swing % with my other system. Does anyone know the method which the Vicon uses to caluclate all the parameters?

    Thank you for any replies and help with this.

    Cate

  • #2
    Re: Vicon Nexus - Generating gait cycle parameters

    Cate,
    I investigated this last year. There were discrepancies but someone at Vicon has the answer. Its a difference in how the they calculate it. Someone on the west coast (CA) was doing a similar investigation as you. Have you called Vicon? It seems like I haven't given you much but they might track the answer down in their system with this info.

    Scott

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    • #3
      Re: Vicon Nexus - Generating gait cycle parameters

      Originally posted by cattmacleod View Post
      Hi

      I am using Vicon plug-in-gait as a means of validating another gait analysis device. I have been unable to find out how the Vicon actually caluculates the gait parameters and specifically how it caluculates distance. I have generated the gait cycle parameters by manually inputing the gait cycle events as I need the calculations to be made over a larger distance than covered by the force plate. The data has been interesting with large discrepency between stance % and swing % with my other system. Does anyone know the method which the Vicon uses to caluclate all the parameters?

      Thank you for any replies and help with this.

      Cate
      I may be able to help here, having worked on this a few years ago. The distance parameters (step length, stride length and walking speed) are based on a specific marker position - by default the toe marker (LTOE for the left side, RTOE for the right), though this can be changed in the Options.

      Stride length is simply the distance from the marker's position at the time defined by the first foot strike event of the gait cycle to the marker's position at the second foot strike event. Walking speed is calculated from this.

      Step length is the distance from the contralateral marker's position at the time defined by the contralateral foot strike event to the ispilateral marker's position at the second ipsilateral foot strike event, projected onto the stride vector as defined for the stride length. In other words, step length does not reflect the lateral distance between the feet.

      When the parameters are calculated in Vicon Nexus or Workstation, these are based on the first cycle for each side where all the necessary events are found - i.e. ipsilateral strike+off+strike and contralateral off+strike. NB! This means that if your first defined gait cycle does not contain a foot off for the contralateral side, the parameters will be calculated based on the second cycle for this side.

      Vicon Polygon can re-calculate the parameters (depending on what preferences you have set up), in which case these can be based on either the first cycle as above, or the average of all defined cycles.

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