## 4 Discussion
The gait parameters of step length, step width and cadence can also be monitored and improved by Kinect-based protocols. Several tests, e.g., the Matthias posture test and rotator cuff mobility and strength test, are potential diagnostic routes that would benefit from the improved accuracy of Kinect. Furthermore, recent studies reported Kinect exergames to have a significant positive effect on balance performance in elderly people [45]. Kinect Azure provides an opportunity in the field of marker-less motion analysis, though it has several limitations compared to classical marker-based motion capture systems, which can provide more extensive and accurate data regarding human motion through selected marker points of the body. Undisputed advantages of the marker-based systems are that the experts can precisely follow the movements of extremities and segments through markers or sensors adhered to the skin over well-defined anatomical locations. The disadvantage of the Kinect Azure camera is that it can only measure the outer shape of the human body, and it deducts major joints from this large dataset. The Kinect-generated 'joint midpoint' is not an exact anatomical location; however, it can be reliably used in answering questions of joint movements along a single axis such as the SLS test. The cut-off value for normal vs. pathological dynamic knee valgus shift cannot be established at the current phase of research. Future studies should establish reference values for the healthy population in both genders and also for specific pathologies; the aim of the current study was one step earlier, i.e., establishing the appropriate metrics that adequately describe the dynamic valgus phenomenon and what can be reliably measured with a marker-less system. In conclusion, the current study shows that in order to reliably monitor dynamic valgus of the knee, medio-lateral shift of the knee over foot at a fixed squat depth is far more suitable than the previously suggested Q-angle at the lowest point of a squat. This variable can be automatically recorded with a marker-less optical camera and software system, allowing a novel diagnostic tool for evaluating osteoarthritis risk factors in the routine orthopedic practice. Future studies may extend the use of this hardware-software combination to follow other joints; however, each joint will require a different set of control measurements and even disease groups. Conceptualization: A.U., E.F. and Z.L. ; methodology: [PERSON] and Z.L. ; formal analysis: [PERSON], Z.L. and M.A. ; investigation: [PERSON], M.K., L.G., G.S. and K.R. ; data curation: [PERSON] and Z.L. ; writing--original draft preparation: [PERSON]; writing--review and editing: [PERSON] and M.A. ; visualization: [PERSON] and Z.L. ; supervision: [PERSON]; project administration: [PERSON]. All authors have read and agreed to the published version of the manuscript. This research received grant funding from the Ministry of Innovation and Technology. Project number: TKP2020-NKA-17. Investment in the Future Program. This publication prepared with the professional support of the doctoral student scholarship program of the co-operative doctoral program of the Ministry of Innovation and Technology financed from the national research, development and innovation fund. The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee of University of Physical Education of Budapest, Hungary (Ethical license number: TE-KEB/No43/2019). Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. The data presented in this study. The authors thank [PERSON] for critically reviewing the manuscript and for providing valuable suggestions on language editing. Moreover, the authors would like to thank [PERSON], [PERSON] and [PERSON], the programmers of Lumio Labs, who helped to develop the Dynaknee software. [PERSON] is a founder of OrthoSera, a startup company that owns intellectual property of the Dynaknee motion analysis software.