Low-Cost Markerless Motion-Capture Systemfor kinematic assessment of postural tests

Maintenance of upright posture is a complex task requiring the center of gravity to reside over a small base of support. Sophisticated neuro-muscular mechanisms are necessary to sustain this position. The postural control system deteriorates with age and disease, balance becomes increasingly tenuous resulting in an enhanced susceptibility to falls. Consequently, it is important to be able to assess the subject’s ability to maintain balance and to be able to predict the risk of falls. In literature there are many clinical balance tests used to predict falls. An example is provided by the Functional Reach (FR) Test, defined as the maximal distance one can reach forward beyond arm’s length while maintaining a fixed base of support in the standing position. The simple clinical measure, extracted from the test, correlates with the risk of recurrent falls in elderly subjects. Nevertheless FR is affected by characteristic flaws of functional evaluation scales, particularly by the ceiling-floor effect, that is a poor sensibility in the middle part of the measurement range. Moreover, FR cannot be considered as a measure of dynamic balance because it is not able to differentiate healthy elders from individuals with balance impairments. More information can be obtained from this motor task if it can be described looking at the kinematic behavior and at the motor strategies employed. Currently, the kinematic assessment is usually provided in laboratory environment with marker-based stereophotogrammetric systems. Ambulatory systems would require different specifications such as: low-costs, easiness of use and non-intrusive techniques. The Motion-Capture system here described, allows to calculate the biomechanical FR index and the relative flex-extension angle between the torso and the thigh of the subject using only one commercial webcam. The technique does not require any physical contact, it results totally non-invasive, and easy to use. It is suited for a 2D analysis of the FR or similar 2D tasks, giving in real-time the expected results, and allowing the contemporary recording of the video signal. Validation tests have been carried out in an indoor and not structured environment.