Concurrent validity of the Microsoft Kinect for Windows v2 for measuring spatiotemporal gait parameters
Introduction
Gait dysfunction is one of the most commonly reported impairments due to aging or acute events such as stroke or musculoskeletal injury [1], [2]. Gait assessment is a way of examining locomotion and body movements in individuals with gait dysfunction [3]. Despite the fact that most clinicians use observational techniques in their assessments, subjective observational evaluations are shown to be insufficient as a reliable approach in clinical settings [4]. Augmenting subjective observation assessments with objective measurements has been shown to strengthen the reliability and accuracy of the gait assessment [3].
Objective analysis in laboratory settings includes collection of spatiotemporal gait and biomechanical data such as velocity, step length and joint and limb motions. Pressure mats, force plates, and three dimensional motion capture systems are common tools used for gait assessments in laboratories. These measurement tools provide essential information about the functional performance of patients and enable more effective targeted treatment and therapeutic interventions [3]. Despite their high accuracy and reliability, the usability of motion capture systems is limited in clinical settings due to high cost, difficulty in the interpretation of captured data [5], [6], and elaborate set up requirements [7]. Pressure mats and/or force plates are more affordable and easier to use in clinics compared with motion capture systems; however, they only measure gait parameters based on foot placements and/or ground contact forces and cannot track other body parts, joint angles, or limb movements. Moreover, pressure mats: (1) limit the subjects to walk within the narrow width of the mat (88 cm) which is challenging for populations with vision impairment, stroke or brain injuries (since they show walking deviation and have difficulty avoiding the sensors on the mat or stepping off the mat [8]); (2) require the clinicians supervising the patients during the walking task to stay off the mat throughout the gait test; and (3) are highly sensitive to the amount of force applied by the subjects to the mat for outputting complete footfall imprints [9].
In the face of above mentioned challenges, the Kinect sensor (Microsoft Corporation, Redmond, WA) provides an opportunity to reconstruct both spatiotemporal gait and joint motion kinematics at a low cost (less than $200) and with minimal setup requirements. By processing captured depth information, the Kinect tracks people and their full body poses within its field of view at the real-time rate of 30 frames per second. Moreover, the Kinect sensor offers additional advantages over the existing gait assessment tools, including the capacity to provide longitudinal and quantitative analysis of gait in private homes. Furthermore, it does not require markers to track joint motions, and consequently will overcome the limitations associated with wearable sensors and 3D motion capture systems. Consequently, researchers have explored using the Kinect sensor for objective gait analysis [10], [11], [12], [13], [14], [15].
The validity and reliability of the older version of the sensor (Kinect for Windows v1) has been thoroughly analyzed and compared against 3D motion capture systems [10], [11], [13], [16], vision-based tracking algorithms [14], [15], and wearable sensors [17] by several research groups.
Recently, a new version of Kinect for Windows (K4W) v2 has been released that provides an expanded field of view, 70.6 × 60 degrees vs. 58.5 × 46.6 degrees in Kinect v1. The new sensor captures images of significantly higher resolution, 6.75 times more color pixels and 2.82 times more depth pixels than the older version, and is capable of tracking 25 body joints of up to 6 people within its field of view, as compared with 20 body joints of up to 2 people in the older version. As a result, it is of great clinical interest to establish the concurrent validity of the K4W v2 to make objective gait measurements and study the sensor’s accuracy and limitations.
The current paper focuses on establishing the criterion validity and test retest reliability of the K4W v2 on gait parameters. The specific objective of this study was to establish the concurrent validity of K4W v2 against the GAITRite mat for measuring the kinematic parameters of gait in healthy subjects, including stance time, step time, step length and gait velocity. The GAITRite mat (CIR systems Inc., Sparta, NJ) is one of the most commonly used pressure sensing walkways, and its reliability in observing and extracting spatiotemporal gait parameters has been established in both younger and older subjects [18]. The presented results could allow researchers in the gait and balance rehabilitation field to use K4W v2 as a valid clinical tool and also to employ it in longitudinal gait analysis studies in the home environment.
Section snippets
Study description
Twenty (20) healthy young adults with no history of medical, mobility or chronic musculoskeletal disorders (mean ± standard deviations; age: 28.8 ± 7.1 years, height: 171.2 ± 10.5 cm and weight: 66 ± 16 kg) were recruited to participate in this study. Ten (10) participants (50%) were woman. Data collection took place at the Balance Mobility and Falls Clinic (BMFClinic) in the Toronto Rehabilitation Institute-UHN University Centre. This study was approved by the Research Ethics Boards at the
Results
Since no asymmetries in walking were apparent in our healthy participants, spatiotemporal parameters from all sequences captured by the two Kinect sensors for each participant were combined and averaged for the left and right sides. Average spatiotemporal data were used for comparison analysis. The comparison results between the K4W v2 and GAITRite in terms of the group mean differences, Bland–Altman 95% limit of agreement and correlation coefficients for three types of walking (usual pace,
Discussion and limitations
This study presents the first attempt to evaluate the accuracy of the Kinect for Windows v2 to measure spatiotemporal gait features in comparison with the GAITRite mat. The K4W v2 is a cost effective and easy to use sensor. Along with the algorithm used in this study for measuring gait parameters, the K4W v2 is a good candidate for making objective full gait assessments to provide more effective targeted treatments and therapeutic interventions in gait. It is therefore very important to study
Conflict of interest
No conflict of intrest.
Acknowledgment
The authors would like to thank Ms. Bing Ye for her assistance in acquiring the data presented. The authors would also like to thank the Balance, Falls and Mobility Clinic at the Toronto Rehabilitation Institute for providing us with required equipment and facilities throughout the study. Study funding was provided by the Toronto Rehabilitation Institute-University Health Network. The authors would also like to thank Marge Coahran for proofreading the article.
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