Comparison of Standing, Prone, and Sitting Protocols for Knee Joint Position Sense Testing in Non-Athletic Adolescent Females: A Non-Weight-Bearing Open Kinetic Chain Study

Background/Objectives: Knee joint position sense (KJPS) assessment lacks standardized testing protocols, and it remains unclear how commonly used non-weight-bearing protocols—standing, prone, and sitting—and target angle influence reproduction error. This study aimed to compare KJPS error across these three protocols and three target knee-flexion angles (30°, 45°, 60°) in non-athletic adolescent females. Methods: In this within-subjects study, 30 non-athletic female participants aged 15–18 years (16.47 ± 1.04) performed an active angle-reproduction task with the tested limb non-weight-bearing, recorded using a VICON motion analysis system. Absolute Error (AE) and Constant Error (CE) were calculated, together with the between-participant dispersion of CE (SD-CE). Results: AE showed a significant main effect of protocol (F = 4.33, p = 0.018, ηp2 = 0.130), confirmed by permutation testing, but no significant angle effect or interaction. Sitting produced lower AE than prone testing (mean difference = 2.98°, Holm-adjusted p = 0.023). CE was significantly positive in all nine conditions, confirming a systematic tendency to overshoot the target angle. SD-CE was lowest in sitting, intermediate in standing, and highest in prone. Conclusions: Testing protocol influenced KJPS accuracy and between-participant dispersion, whereas no target-angle effect was detected within the tested protocol configurations. The sitting protocol emerged as a promising candidate for further reliability and standardization research in this population.