Automatically assess foot strikes

In clinical gait trials for kinetic analysis involving one or more force plates, Vicon Nexus can automatically provide an indication of whether or not the foot is correctly positioned and is producing valid data for your live trials. Nexus displays this information on screen. This can save you time when you are assessing each foot strike to decide whether it is valid.

As each strike is detected or is determined to be invalid, the box representing the force plate in the 3D Perspective view or in the Camera view for a video camera, turns the appropriate color:

• Red: left foot strike
• Green: right foot strike
• Dark gray: invalid strike

Counters on either side of the force plate box show how many valid strikes have been detected for each foot during the current session.

To auto-detect foot strikes:

1. Before you begin, ensure that you have:
   
   • Calibrated the Vicon system.
   • Applied the appropriate marker set to the subject.
   • Ensured that you have a valid subject in Nexus.
   • Connected and configured one or more force plates.
2. On the Window menu, click Footstrike Monitor Settings and in the dialog box, ensure the options for foot strikes are as required:
   
   1. Maximum strikes: Maximum number of foot strikes per side that are added to the count in a single trial
   2. Force Threshold: Minimum force required on force plate to produce foot strike
   3. Marker Height Threshold: Minimum height of foot marker above force place for foot to be recognized for foot strike
   4. Left and Right Foot Markers: Comma-separated list of names of one or more markers that define the segment (i.e. foot) that will strike the plate.

   5. Reset footstrikes button: Enables you to reset the foot strike counters.

      

3. In the Options dialog box (press F7), ensure that Footstrikes is selected and that the options for Show in 3D Perspective (for optical cameras) and Show in Video Cameras (for video cameras), Font Size, Opacity, and Background Color are as required.

To reset foot strike counters:

• Right-click anywhere in the workspace and then click Reset.

or

• Press CTRL+SHIFT+R

Using multiple foot plates

If your trial requires multiple force plates, they are laid out in the order of the force plate IDs (that is, FP1 is furthest left/uppermost depending on the position of the force plate box).

Strikes straddling two force plates are marked invalid. However, if required they can be processed by the Process Dynamic Plug-in Gait Model pipeline operation, by selecting the Allow cross-plate strikes option.