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Example: Road environment
When applying ‘the road’ environment, the variables to record differ for the ‘classical road’ and the ‘interacting road’. When performing the ‘classical road’, the patient is standing on the platform with solely the goal of maintaining balance. When the ‘interacting road’ is performed by the patient, the patient not only has to maintain balance whilst moving over the bumps, the patient also has to hit moving objects with the hands.
Road without interaction
When a patient performs the road without interaction, common variables that are set by the operator are:
- Playback speed of the road’s progress
- Scale factor for the platform motions
- With / without stereo projection
- With / without ego-motion
These variables are recorded also for post processing. Next to that, theplayback speed and scale factor are important aspects indicating progression of balance control. Independent of the settings of the environment, the patient might show more or less problems for maintaining balance. Variables that are recorded provide enough information for defining balance performance.
Variables that contain valuable information and are recorded are basic aspects like the required number of ‘steps out’ for balance correction, the position of the hands (alongside the body or sideways raised) and stance width are good indicators for balance. The variables that are recorded should allow post processing of these variables.
Next to deriving information from the number of steps, the position of the hands and the stance width, it is commonly assumed that a shift from ankle to hip strategy occurs when the subject faces major balance problems (for instance when perturbed). Measuring the direction of motion of the legs and trunk provide information for defining if legs and trunk are moving parallel or opposite. When moving parallel, the ankle strategy is used whereas the hip strategy is performed when the legs and trunk are moving in opposite direction.
Not only motions of the body contains valid information about balance and postural control, force plate data is frequently used during quite standing for defining postural control. Some variables that are derived from the force plate data are surge/sway (and velocities), centre of pressure and frequency analysis as indication for balance performance. However, it is unclear if these variables can be used for ‘the road’ and precaution is required.
Data collection
Independent of the type of post processing, it is necessary that both the motion capture-, analog- and platform data are collected appropriately.
It is essential that the recorded data is fully synchronized in time. For ease of use, matching sampling frequency is preferable.
When performing the road (classic or with interaction), the actual recording of the balance when performing the road is being preceded by a reference recording. To prevent overwriting of data, it is suggested to use the time stamp option of the record module for distinction between the 2 files and use the windows folder structure for defining patient and session.
Road with interaction
Distinction that needed to be made between the 2 roads has got to do with the fact that with the ‘road with interaction’, the hands are not solely used for maintaining balance, but also for hitting moving balls. Therefore, the hand data can’t be used in the same way as was the case for the ‘classic road’. However, the interaction provides a lot of possibilities for analysis. Most straightforward is counting the number of hits. Other possibilities that can be measured are defining the distance the hands have moved, the envelope they’ve moved in, the max velocities etcetera.