Validity and reliability of the Kinect within functional assessment activities: Comparison with standard stereophotogrammetry B. Bonneche` re a, *, B. Jansen b,c , P. Salvia a , H. Bouzahouene a , L. Omelina b , F. Moiseev a , V. Sholukha a , J. Cornelis b , M. Rooze a , S. Van Sint Jan a a Laboratory of Anatomy, Biomechanics and Organogenesis (LABO), Universite´ Libre de Bruxelles, CP 610, Lennik Street 808, 1070 Brussels, Belgium b Department of Electronics and Informatics – ETRO, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium c iMinds, Dept. of Future Media and Imaging (FMI), Gaston Crommenlaan 8 (Box 102), B-9050 Ghent, Belgium 1. Introduction Human motion tracking is widely used for movement analysis within a variety of purposes including rehabilitation and biomechanical representation of human motions [1]. Functional assessment has proven to be useful in clinics during rehabilitation [2]. Currently, most clinical motion analysis centers use a marker- based system (MBS) [1]. Although the MBS validity is high with respect to the positions of the markers in 3D space [3], some problems occur with MBS in daily practice: accuracy and mainly reproducibility of such a system is still controversial for the estimation of joint centers and relative segment orientations [4]. This can be explained by the fact that small errors in marker placement and soft tissue artifacts are causing larger errors in the estimation of the joint centers [5] and the relative segment orientations [6–9]. As such, marker setting is time-consuming and therefore not always suitable for young children and for patients not able to stand for a long period of time. Due to the high price and poor transportability of MBS, analysis must be performed within specialized departments. Such MBS analysis is therefore difficult to perform at the patient’s home by a therapist. Note that despite the above-recognized error sources, MBS has been used in this study as reference system because it is largely adopted in the motion field. Markerless systems (MLS) are being developed for nearly 20 years [10]. They seem promising and open perspectives for complementary usages with respect to MBS analysis. Moreover, MLS shows an interesting perspective for functional assessment because the drawbacks due to marker placement are not present. MLS are usually less cumbersome than MBS and less expensive. To the authors’ knowledge MLS systems are unfortunately not widely used for functional analysis yet, probably because of the lack of dedicated hardware, related software and validation studies [10– 15]. The recent availability of the Kinect TM sensor (based on PrimeSense Technology, Tel Aviv, Israel) [16–18] opens up interesting perspectives for functional analysis of patient assess- ment. This cost-effective and portable device is combining a regular color camera with a depth camera (consisting of an infrared laser projector and an infrared camera) and built-in software to detect a simple skeleton based on advanced pattern recognition methods [19] (note that due to the commercial nature of this hardware, no information on the underlying recognition can be found in the scientific literature). Before using this new hardware as MLS for functional assessment, scientific validation is required. No extensive Gait & Posture 39 (2014) 593–598 A R T I C L E I N F O Article history: Received 31 January 2013 Received in revised form 27 June 2013 Accepted 25 September 2013 Keywords: Motion analysis Markerless motion capture Biomechanics New technology A B S T R A C T The recent availability of the Kinect TM sensor, a cost-effective markerless motion capture system (MLS), offers interesting possibilities in clinical functional analysis and rehabilitation. However, neither validity nor reproducibility of this device is known yet. These two parameters were evaluated in this study. Forty-eight volunteers performed shoulder abduction, elbow flexion, hip abduction and knee flexion motions; the same protocol was repeated one week later to evaluate reproducibility. Movements were simultaneously recorded by the Kinect (with Microsoft Kinect SDK v.1.5) MLS and a traditional marker- based stereophotogrammetry system (MBS). Considering the MBS as reference, discrepancies between MLS and MBS were evaluated by comparing the range of motion (ROM) between both systems. MLS reproducibility was found to be statistically similar to MBS results for the four exercises. Measured ROMs however were found different between the systems. ß 2013 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +32 2 555 6262. E-mail address: bbonnech@ulb.ac.be (B. Bonneche` re). Contents lists available at ScienceDirect Gait & Posture jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/g aitp os t 0966-6362/$ – see front matter ß 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gaitpost.2013.09.018