The health and safety of the participant is paramount during any testing. Informed consent should always be obtained from the participant (see BASES Code of Conduct in Appendix 1) and completion of a health questionnaire is often required. Sufficient time must be allocated for a warm-up and for the participant to become fully familiar with the testing environment and testing conditions.
The clothing worn by the participant should allow the limbs and body landmarks relevant to the analysis to be seen clearly. The careful placement of small markers on the skin can help the analyst to locate body landmarks during digitising, but the positioning of these markers must be considered carefully. Movement of soft tissue means that surface markers can only ever provide a guide to the structures of the underlying skeleton.
Markers are often used to help identify the location of a joint’s instantaneous center of rotation. Whilst a single marker can adequately represent the axis of a simple hinge joint, more complex joints may require more complex marker systems (see Chapter 3 for more detail on marker systems). The number of trials recorded will depend on the purpose of the analysis and the skill level of the participants.
As the movement patterns of skilled performers are likely to be significantly more consistent than those of novice performers (Williams and Ericsson, 2005), they may be required to perform fewer trials in order to demonstrate a typical performance. During the filming it is often useful to record a board in the field of view, showing information such as the date, performer, trial number and condition, and camera settings.
Many of the procedures described in the previous section for two-dimensional video analysis will also apply when using a three-dimensional approach (selecting an appropriate frame rate, shutter speed and aperture; ensuring correct lighting of the performer; maximizing the image size and focusing the camera manually). This section will discuss the main issues that must be considered at the recording stage of a three-dimensional analysis.