Handling Strategies
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Group- vs. Individual-Oriented BSP Handling Strategies
Common vs. Trial-Specific BSPs
Segment IDs

Group- vs. Individual-Oriented BSP Handling Strategies

The group-oriented approach has been used almost exclusively in the general-purpose motion analysis packages including Kwon3D 1.0 (released in 1991). In other words, the BSP ratios (CM to segment-length ratio, mass to whole body mass ratio, & radius of gyration to segment length ratios) are registered in the model file and applied to all the subjects or trials. Several problems have been encountered in this approach:

The group-oriented approach can not accommodate any foreign object the mass & moments of inertia (MOIs) of which vary from one trial to another, and from one subject to another. In the worst case, one must create a model file for each trial.
The group-oriented approach does not allow individualization of the BSPs since it is based on the BSP ratios.

In order to overcome these problems, one must use an individual-oriented BSP handling strategy. The best way to do this is to separate the BSP data from the body-model file and store them in the so-called BSP files. A BSP file can contain either the group-oriented BSP ratios or the individualized BSP data. In other words, the approach to be used depends on the nature of the BSP file: group-oriented or individual-oriented. The BSP data can be read into the trial file from the specified BSP file.

Several BSP estimation methods are listed under BSP Estimation Methods. The degree of individualization varies from one method to another. See the individual method pages for the details.

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Common vs. Trial-Specific BSPs

One problem not completely solved yet with the individual-oriented approach is the trial-specific BSPs. This is mainly due to the use of foreign object segments. When the subject uses tools such as racquet, bat or barbell as a part of the body, these must be included in the model. For example, if one wants to see the effects of barbell weight on the lifting technique and the weight of the barbell changes from one trial to another, the inertial properties of the barbell, thus, are trial-specific. To accommodate this need, one must create a BSP file for each trial, which is not quite desirable. Here are the solutions:

Store all the common BSPs in the BSP file.
House a BSP editor in the program (at the trial level) to allow editing of the BSP data. Enter the trial-specific BSPs in this editor environment.
Set up the editor to accept both the BSP ratios and the actual BSP data. This will allow the investigator to use the trial-specific BSPs in combination with either the group-oriented or the individual-oriented BSP handling strategy.

The combination of group/individual-oriented strategy and the common/trial-specific BSPs prevents investigators from creating multiple BSP files for the same subject or subject group. Starting from Version 2.0 (released in 1993), Kwon3D uses these strategies and allows flexible BSP handling.

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Segment IDs

Separation of the BSP data from the body model causes one minor problem. While reading the BSP data into the trial file from the BSP file, the analysis program must be informed of the types of segments included in the model. The segment name used in the modeling process do not necessarily inform the program of the segment types. One way to nicely solve this problem is to use the segment ID numbers. For example, here is the ID # system used in Kwon3D:

ID # Description

0
1-12
13-20
21-30
31-35

Body part: does not require BSPs
Reserved human body segments
User-defined human body segments
Foreign object segments
Imaginary segments

ID # Description
1
2
3
4
5
6
7
8
9
10
11
12
Hand
Forearm
Upperarm
Foot
Shank
Thigh
Head
Thorax
Abdomen
Pelvis
Thorax-Abdomen
Whole Trunk

During the body modeling process, one can specify the segment types by using the ID numbers. The analysis program will then read in the right BSP data from the registered BSP file.

Another important advantage of using the segment ID numbers is the compatibility between the BSP estimation programs and the BSP file. One may use the same ID number system in the BSP estimation programs to secure a complete compatibility among the estimation method, BSP file, and the body model. In other words, the BSP files can be created by the BSP estimation programs, which will then be used by the analysis program.

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Young-Hoo Kwon, 1998-