A low cost real-time motion tracking approach using webcam technology

Abstract

Physical therapy is an important component of gait recovery for individuals with locomotor dysfunction. There is a growing body of evidence that suggests that incorporating a motor learning task through visual feedback of movement trajectory is a useful approach to facilitate therapeutic outcomes. Visual feedback is typically provided by recording the subject's limb movement patterns using a three-dimensional motion capture system and displaying it in real-time using customized software. However, this approach can seldom be used in the clinic because of the technical expertise required to operate this device and the cost involved in procuring a three-dimensional motion capture system. In this paper, we describe a low cost two-dimensional real-time motion tracking approach using a simple webcam and an image processing algorithm in LabVIEW Vision Assistant. We also evaluated the accuracy of this approach using a high precision robotic device (Lokomat) across various walking speeds. Further, the reliability and feasibility of real-time motion-tracking were evaluated in healthy human participants. The results indicated that the measurements from the webcam tracking approach were reliable and accurate. Experiments on human subjects also showed that participants could utilize the real-time kinematic feedback generated from this device to successfully perform a motor learning task while walking on a treadmill. These findings suggest that the webcam motion tracking approach is a feasible low cost solution to perform real-time movement analysis and training.

Keywords: Gait; Kinematics; Motion tracking; Motor learning; Real time.

Figure 1

(A) Schematic representation of real-time tracking set-up. (B) Schematics of target-template and (C) tracking error computation.

Figure 2

Hip and knee joint kinematics recorded using the webcam tracking approach from four subjects on two consecutive days.

Figure 3

(A) Example of target-tracking performance from a subject at the beginning (block 1) and end of target-tracking practice (block 10). (B) Mean target-tracking error from four subjects during each block of training on two consecutive days. Target-tracking error is shown as % error observed during block 1 of practice on Day 1. Dotted vertical line separates performance on Day 1 and Day 2. Error bars represent standard error of the mean.