Video Movement Analysis Using Smartphones (ViMAS): A Pilot Study

The overall goal of this study is to test the concurrent validity of kinematic measures recorded by the smart phone application, and compare them to measures recorded by a 3D motion capture system, in order to develop a valid clinical protocol. This clinical protocol has been developed, so that the smartphone can be used to capture human movement, and provide valid kinematic measurements, using a simple and user-friendly set-up. The main advantage of this technique is that the smartphone can be set up in a clinic or a patient's home, for video analysis of human movement.

Visual demonstration of this method is critical, because clinicians can follow the step-by-step clinical protocol, in order to obtain valid measures of lower extremity kinematics. Demonstrating the procedure will be graduate students, who are coauthors in the study. Begin by measuring and marking off a six-meter walkway, using measuring tape and sticky tape.

Then place four 3D motion capture cameras at the four corners of the six-meter walkway, to record walking in this area. Orient each of the cameras at the diagonal ends of the walkway to face each other. Next, escort the participant into the testing area, and collect weight and leg length, from the greater trochanter to the medial malleoli of both legs with a measuring tape.

Then measure the height by having the participant stand barefoot next to a measuring tape, attached to the wall. Place a ruler on top of the participant's head to read the measurement from the measuring tape adhered to the wall. Mount the smart phone on a tripod, using an adapter clip to hold the smart phone.

Place the tripod perpendicular to the center of the walkway, at 2.0 meters away from the first setted trial. Note the tripod should be placed at 4.0 meters away for the second set of trials. Then calculate the height from the floor to the camera lens in meters for each configuration, using the patient's leg length.

The near camera position, two meters, is for recording and analyzing only the lower extremity movement whereas the far distance covers both lower extremity and trunk. Next, place clusters of three smart markers with velcro straps on the bilateral anterior superior iliac crest or ASIS, upper one-third of the lateral aspect of the thighs, upper one-third of the lateral aspect of the calves, and the dorsum of both feet. Place a single smart marker on the midline between the right and left posterior superior iliac spines.

Place stickers indicating bony landmarks of the bilateral medial and lateral femoral condyles, medial and lateral malleoli, and the webbed space between first and second toes for calibration of the 3D motion capture system. Finally, calibrate the equipment using an instrumented wand with smart markers on it, to register the 3D location of the stickers. To begin, have one investigator operate the smartphone, and the other operating the computer that controls the 3D motion capture system.

Ask the participant to complete a practice trial. Then, open the smartphone application and press the red record button on the bottom center of the screen to begin recording. Use numbered paper to indicate trial number on the smartphone recording.

Then, instruct the participant to walk at their normal pace, and to focus on a marker placed on the opposite wall to assist in walking in a straight line. Give the participant a countdown to start by saying three, two, one, go. Then, have the participant cross the first two 3D motion capture cameras placed at the beginning of the walkway on either side, and walk towards another two cameras placed at the other end of the walkway on either side.

After the subject finishes walking the six meter distance, countdown to the end of the trial by saying three, two, one, stop. Then press the red record button once more to stop recording the walking trial. Check all markers for position after each trial.

Next, move the tripod with the smartphone to the second distance four meters away to capture the upper and lower body. Ask the participant to stand on the midpoint of the walkway, then start walking in the same manner as before. Finally, save and verify the 3D motion capture recordings and smartphone recordings.

Then remove the smart markers. Begin by manually recording the knee angle that is displayed on the screen at the heel strike and toe off phases of the gait cycle. Then, complete the analysis of smart phone recordings for heel strike and toe off events.

Use the stylus for increased accuracy of landmark placement for knee angle measurements. Next, view that was just recorded by selecting the video square in the bottom left corner of the screen. Use the scrollbar at the base of the screen to select the frame in which the subject is closest to heel strike or toe off in the center of the screen.

Then, to drop in the angle, tap on the white outline pencil icon on the upper right side of the screen. Select the angle option in the drop down menu. Choose a preferred color and the angle marker.

Slide or tap the stylus anywhere on the screen to drop in the angle. Finally, place the center of the angle on the knee joint, with the vectors reaching upwards along the femur and downwards towards the lateral malleoli. If needed, zoom in by placing two fingers close together in the center of the screen and slowly drawing them apart from one another.

Based on the results, there was a significant difference between the angle measurements by the 3D motion capture system and smartphone application. The plots for the 4.0 meter and the 2.0 meter distances displayed data that are more scattered around the mean difference line in the center. This indicates that the camera position did not contribute to the errors in measurements.

While attempting the clinical protocol for smartphone video movement analysis, it's important to remember that the camera must be placed at the set distance and the height of the camera is determined by the individual's leg length.