Validity and Reliability of a Depth Camera-based Automated Physical Function and Fall Risk Assessments

For the Tandem Stance Test comparisons, the Azure Kinect-based Tandem Stance Test system quantified the distance traveled by the pelvic point to X, Y, and Z coordinates over a 30-second duration while the physical therapist measured the time elapsed until the participant lost balance was measured with a maximum of 30 seconds. Participants remained a tandem stance, positioning their preferred leg in front such that the heel of the front foot touched the toes of the back foot, ensuring both feet were aligned as straight as possible. They stood with holding on to two chairs each placed on their sides for stability and safety. Upon the cue to 'start', the participants let their hands go and both the Azure Kinect-based system and the physical therapist's stopwatch initiated their measurements. Participants tried to maintain their stance for 30 seconds. The participants had to reposition themselves when they stepped, used hands or lose balance for 30 seconds

The Five Times Sit-to-Stand Test (FTSS), standardized by Csuka and McCarty, has been designed to assessing lower limb strength as well as balance and postural control among elder population with high level of reliability. A previous study reported excellent intra-rater reliability (ICC=.914-.933) and inter-rater reliability (ICC=.988-.995) among healthy older adults. In addition, Five Times Sit-to-Stand Test more than 11.50 seconds had been reported to represent risk of falls among elders over 65-year-old. To assess Five Times Sit-to-Stand Test , a chair, 45cm in height and fixed to the ground, was placed three meters from the camera. Participants began seated, and on start cue, repeatedly stood up and sat down five times. The Azure Kinect-based system automatically ended its measurement as the participant completed the fifth stand, whereas the physical therapist manually measured time using the stopwatch. The time measures from the system and therapist were compared.

The Timed Up and Go test (TUG) has been employed as a straightforward assessment of an individual's mobility, necessitating both static and dynamic balance. A Timed Up and Go test duration exceeding 9.50 seconds has been identified as indicative of a heightened fall risk in individuals aged 65 and older. A previous study reported excellent intra-rater reliability (ICC=.97) and inter-rater reliability (ICC=.96). Initiating in a seated position, participants stood upon commencement of the test. Simultaneously, the Azure Kinect-based system and stopwatch began the time measurements. Participants then walked a distance of three meters, turned around, retraced their steps, and resumed their seated position. The Azure Kinect-based system automatically terminated its timing once the participant was seated, while the physical therapist manually stopped the stopwatch. The time measures from the system and therapist were compared.

The assessment includes three tests: a Timed Up and Go test test where participants walked a distance of 3 meters at their comfortable pace; a Five Times Sit-to-Stand Test which the duration is also measured; and the standing balance test which determines a participant's capacity to maintain three different stances of side-by-side, semi-tandem, and full tandem, each for 10 seconds.

Participants are scored on a 5-point scale for each task, where a score of 0 signifies an inability to perform, while a 4 denotes independence in execution. A perfect score of 56 is a marker of excellent balance. Administering the Berg Balance Scale is efficient, taking between 10 to 20 minutes, and requires only basic equipment such as a chair, stopwatch, ruler, and step within a small space.

Participants, standing barefoot, aligned the side of their body with a wall, ensuring no contact. Their stance was parallel with feet comfortably spaced. With their shoulders flexed at a 90° angle adjacent to the wall, they kept their elbows straight and hands clenched. The starting point on a horizontally affixed measuring tape, level with the floor, was determined by where the third metacarpal touched. This tape was aligned with each participant's acromion height. Without taking a step, lifting heels or losing balance, participants leaned forward to their maximum extent. The difference between the initial and final third metacarpal positions on the tape denoted the reach distance.

During the Four-Square Step Test, participants were instructed to step over four straight tapes, each 90 cm in length, laid out in a cross-shape configuration on the floor. Beginning in square 1 and facing square 2, participants followed a specific sequence: they stepped forward into the next quadrant, then to the right, backward, and finally to the left, moving in a clockwise direction. This sequence was then retraced in a counterclockwise manner. It was essential for both feet to touch down in each quadrant. Participants aimed to complete this pattern as fast as they could, avoiding stepping the tapes. The duration taken to finish the sequence was recorded.

The strength of the dominant hand's maximal grip force, indicative of upper extremity muscle strength, was gauged using a digital isometric hand dynamometer.