Do Different Two-Dimensional Camera Speeds Detect Different Lower-Limb Kinematics Measures? A Laboratory-Based Cross-Sectional Study

<b>Background/Objectives:</b> Football poses a high risk of sustaining lower-limb injuries, particularly anterior cruciate ligament (ACL) injuries, owing to the frequent jumping and landing movements. Identifying risk factors for these injuries is crucial to successful prevention. Two-dimensional (2D) video analysis is a commonly employed tool for assessing movement patterns and determining injury risk in clinical settings. This study aims to investigate whether variations in the camera frame rate impact the accuracy of key angle measurements (knee valgus, hip adduction (HADD), and lateral trunk flexion (LTF)) in male football players during high-risk functional tasks such as single-leg landing and 45° side-cutting. <b>Methods:</b> This laboratory-based cross-sectional study included 29 football players (mean (SD) age: 24.37 [3.14] years). The frontal plane projection angle (FPPA), HADD, and LTF during single-leg landing and side-cutting tasks were measured using two different camera frame rates: 30 frames per second (fps) and 120 fps. The 2D kinematic data were analyzed using Quintic Biomechanics software. <b>Results:</b> Significant differences in FPPA scores during single-leg landing were observed between the 30 fps and 120 fps for both the dominant (mean difference = 2.65 [95% confidence interval [CI]: 0.76-4.55], <i>p</i> = 0.008) and non-dominant leg (3.53 [1.53-5.54], <i>p</i> = 0.001). Additionally, the FPPA of the right leg during the side-cutting task showed significant differences (2.18 [0.43-3.93], <i>p</i> = 0.016). The LTF of the right leg during side-cutting displayed a significant variation between frame rates (-2.69 [-5.17--0.22], <i>p</i> = 0.034). No significant differences in HADD were observed. <b>Conclusions:</b> Compared with a 30 fps camera, a high-speed (120 fps) camera demonstrated a superior performance in delivering accurate kinematic assessments of lower-limb injury risk factors. This improved precision supports injury screening, rehabilitation monitoring, and return-to-play decision-making through determining subtle biomechanical deficits crucial for lower-limb injury prevention and management.