###### Abstract  
The accurate and reliable measurement of hip flexion angles during the Straight Leg Raise (SLR) test is essential for clinical and research purposes. Despite the widespread use of motion analysis tools, few studies have examined the reliability of affordable, open-source software 0.9.5 like Kinovea for this application. This study aimed to evaluate the intra- and inter-examiner reliability of Kinovea for measuring the hip flexion angle during the SLR test in individuals with and without low back pain (LBP). An observational study was conducted involving 53 participants (38 with LBP and 15 asymptomatic controls). Each participant underwent two SLR test sessions conducted by two examiners with varying levels of experience. The hip flexion angles were measured using Kinovea software based on video recordings. Intra- and inter-examiner reliability were assessed using the Intraclass Correlation Coefficient (ICC), Standard Error of Measurement (SEM), and Minimal Detectable Change (MDC). The effects of examiner experience and patient group were also analyzed. Kinovea demonstrated excellent intra- and inter-examiner reliability for measuring hip flexion angles, with ICC values ranging from 0.985 to 0.998. The SEM values were low (0.5\({}^{\circ}\)-1.5\({}^{\circ}\)), and the MDC values at 95% confidence ranged from 1.3\({}^{\circ}\) to 4.0\({}^{\circ}\). No significant differences were found between the examiners' experience or the patient groups. Thus, Kinovea offers a reliable, cost-effective, and user-friendly method for measuring hip flexion angles during the SLR test. Its consistency and precision, even across examiners with differing experience levels, highlight its potential to standardize assessments and improve diagnostic and therapeutic applications. Future research should explore its use in more complex movement analyses and diverse clinical populations to further validate its utility. low back pain; kinovea; reliability; range of motion 2025154520202420251545202024 Among the most robust and scientifically validated tools for kinematic analysis are three-dimensional (3D) motion analysis systems, which provide highly precise data. However, these systems are often costly and require complex setups and specialized expertise [2]. These limitations have led to the development of newer, more affordable two-dimensional (2D) technologies, some of which have demonstrated comparable precision to high-end 3D systems at significantly lower costs (approximately GBP 700 or EUR 950, as reported by [PERSON] et al. [3]). Before such technologies can be adopted for standardized assessments--such as evaluating clinical tests like the Straight Leg Raise test--it is crucial to establish their validity and reliability. One affordable option is Kinovea, an open-source 2D motion analysis software released under the GPLv2 license in 2009 through the collaboration of researchers, coaches, athletes, and programmers worldwide. Kinovea enables the analysis of distances, angles, coordinates, and spatial-temporal parameters [4] by evaluating video recordings frame by frame. It allows calibration even in non-perpendicular planes relative to the camera's perspective, offering versatile applications. Kinovea has been employed across sports science [5], clinical research [6], and as a comparative tool to study other technologies [7]. Kinovea stands out for being free, user-friendly, and portable, making it suitable for real-world applications without requiring prior technical expertise to obtain reliable measurements [8]. Although the software has been validated for some temporal measurements, studies examining its reliability in specific clinical tests, such as the Straight Leg Raise (SLR) test, remain scarce. This SLR test is commonly used to identify radicular pain by mechanically provoking irritated lumbosacral nerve roots, usually associated with lower back pain and lumbar disc herniation [9; 10], as supported by biomechanical evidence [11].