Gait

Categories

APAS/Gait Online Manual

[ Tutorial | Quick Guide | Lab Setup | Virtual Lab ]

Welcome to APAS/Gait version 1.04 - Revision 2004.10.21 . This software module allows you to analyze and visualize 3-dimensional gait data based on standard marker sets. Results can be reported in standard gait analysis reports, but we also encourage you to analyze the 3D nature of the data in a virtual world.

Marker sets that are currently supported are: Helen Hayes (original and modified), and Keith Vaughan (original and modified). We plan on adding new marker sets periodically, so if you have any suggestions, please do not hesitate to contact us.

This user's manual describes a typical  'flow' of events that you may follow while doing a gait analysis. However, the system is flexible, and allows you to go back and forth, adjust parameters, or even compare different models.

Analysis

APAS/Gait uses the concept of an analysis. An analysis is one trial or one gait analysis.

An analysis can be started by choosing a data set of kinematic data. In the Analysis window, open a dynamic trial file (by using the button on the right of the General tab):

Immediately after opening the dynamic trial file, APAS/Gait will analyze this data and choose a default marker set (method) that is supported by the data. Check here for the marker sets that APAS/Gait recognizes. Any method that is supported by the data can be chosen in the method drop down list. When selecting a different method, APAS/Gait will recalculate the model and update the 3D window and all other open windows. 

Note: Selecting a different marker set may result in slightly differently sized bones in the 3D display. This is caused by the underlying model: for each marker set, the estimated joint centers may be different. APAS/Gait will always scale bone geometry dynamically to match your markers and joint centers. In other words, the visualization represents your actual data, and has not been "constrained" by a skeletal model.

After opening a dynamic file with a valid marker set, the results in the renderer window should look similar to this:

Navigating the scene

The scene can be navigated using the mouse. For this place the mouse pointer anywhere in the scene and move the mouse while holding a mouse button down. Different mouse buttons have different effects:

We realize this takes a little practice, but you'll find it's a very convenient way for navigating the scene. If you "get lost" or cannot return to the position you had in mind, you may want to use the Reset-button at the bottom-right of the control panel (or the navigation controls, see below).

Navigation controls

In addition to using the mouse, the scene can also be navigated using the navigation controls. This Navigation Controls window can be opened from the menu (Options - Navigation Controls...) or from the control panel at the bottom of the main window (Controls...).

Use the camera position buttons to choose a preset orientation to look at your model. There are 9 preset positions, from the front of the model going all the way around it. There is also one preset camera position to view the model from above.

Additionally, the sliders can be used to move the whole scene in the desired direction.

Inverse Dynamics

Under construction ... check here for force plate setup.

Anthropometry

All marker sets need specific anthropometric measurements to calculate joint centers. These measurements are what "drives" the model. 

When first opening a .3d file, APAS/Gait will use default settings and indicate which settings are actually used in the chosen method (marker set); all anthropometric properties that APAS/Gait uses in calculating the model have the "Used" column checked (see Analysis window - Anthro tab). 

Note: the values shown are defaults and should be edited to match your measurements. As soon as a value is changed, APAS/Gait will automatically recalculate and update the model in the background. All calculated results are immediately updated throughout APAS/Gait, including the renderer window, and any charts, or reports. 

In the example shown below, only the radius marker will have any effect on the model calculations. It is nice to  check the influence of this setting by changing it from 0.01 m (1 cm) to 0.03 m (3 cm) and see how it changes the results in the 3D window (and any open charts and reports). We suggest to have both the markers and joint centers displayed in the 3D window to appreciate the changes.

Gait Cycle Events

In addition to charting and reporting as a function of time, it is common to display data as a function of identified gait events (either gait cycle or stance phase). In fact this is how data is most commonly reported. 

Before being able to do so, all gait cycle events must be identified for the current analysis (Analysis window - Events tab). 

Make sure to select which foot strikes first in your analysis, and then press any of the buttons (marked RON, LOFF, etc.) to mark the corresponding event. In the bottom right of the screen the current "frame" can be identified. The 3D window should be used for visual verification. Any speed/position slider in APAS/Gait can be used to go through your data, including the one on the bottom of this tab.

3D Display

3D Display settings for the current analysis can be controlled on the 3D Display tab. Choose color and whether or not to display joint centers (default red balls), whether to display the markers, or to display the segments' Local Coordinate Systems (LCS, by a triad of arrows). These local coordinate systems are a good aid for identifying jerks or other strange movement artifacts in the 3D window.

Other settings that can be changed include rendering options and location sliders to reposition the model in the Lab Coordinate System. By default the model will be positioned in the center of the grid. But being able to change the location in the Lab Coordinate System is convenient for comparing multiple analyses in one scene (pre-post, healthy-pathological gait, or even the influence of different marker sets and the effect of anthropometric settings).

Trace Joint Centers

If desired, the path of calculated joint centers can be displayed (traced) in the 3D display. This is a good tool for identifying gait events or visualizing excessive sway. Select the joints centers of interest in the Analysis - Trace tab. 

Traces are color-coded to represent their relative velocity. Darker colors represent slower movement; lighter colors represent faster movement. 

Reports

Custom text to be displayed on reports can be entered in the Analysis - Reports tab, or from the menu (View - Reports). The indicated text fields (Subject, ID, Date, Diagnosis, Comments) will only be used in the reports.

Choose Charts... (or View - Charts... on the menu) to open a chart window. Note that when a different analysis method is chosen (or when used anthropometric settings are changed), any open charts or reports will be automatically updated. The joints and parameters of interest can be selected in the bottom of the screen: 

In order to correlate the chart with the rendered model, the slider in the bottom of the screen can be used (see below). You may need to use the splitter slider at the bottom of the screen to find it. In the bottom of the screen the current position of the left and right sides are shown. This position can be controlled by any position/speed slider in APAS/Gait, including the one in this window.

Choose Report... (or View - Report... on the menu) to open a standard report window. Choose the parameters of interest in the bottom of the screen. The trial information at the top of the report can be modified: Subject, ID, Date, Diagnosis, Comments can be changed in the Analysis - Reports tab of the current analysis. The Custom Title of this report can be changed in the Global Settings, accessible from the menu. 

Note that when a different analysis method is chosen (or when used anthropometric settings are changed), any open charts or reports will be automatically updated.

If desired, data can be browsed using the data browser. Choose the variable of interest with the drop down list boxes in the bottom of the screen.

Note that when a different analysis method is chosen (or when anthropometric settings are changed), any open data browser window will be automatically updated.

Global Settings

Global settings can be changed by choosing this function from the menu. 

Please note that some settings will not take effect until APAS/Gait is restarted.

This page was last modified on 12/13/2002 at 20:14 PST. Copyright © 1994 - 2002, all rights reserved, Ariel Dynamics Inc. Please send your comments or feedback to webmaster@arielnet.com or proceed to our feedback form. This page has been accessed 111 times since Dec 12, 2002. Our privacy policy is here.