Intra- and Inter-Rater Reliability of Primitive Reflex Assessments in Youth Football Athletes

Background: Primitive reflex (PR) assessments based on the Institute for Neuro-Physiological Psychology (INPP) framework are increasingly used in developmental and athletic populations. However, the reproducibility of these observer-based assessments remains insufficiently documented. This study investigated the intra- and inter-rater reliability of subjective PR assessments and examined the potential influence of evaluator expertise in elite youth football athletes. Methods: Sixty-nine male youth football players from an elite academy (age: 18 ± 2 years) participated in this study. PR assessments included the Moro reflex, asymmetrical tonic neck reflex, symmetrical tonic neck reflex, and tonic labyrinthine reflex, evaluated using standardized INPP procedures (0-4 ordinal scoring scale). Intra-rater reliability was assessed by an experienced examiner across three testing sessions performed over six months. Inter-rater reliability was evaluated using standardized video recordings independently scored by two novice raters. Relative reliability was assessed using intraclass correlation coefficients (ICCs) with corresponding 95% confidence intervals (95% CIs), while absolute reliability was quantified using the standard error of measurement (SEM) and the minimal detectable change at the 95% confidence level (MDC95). Results: Good to excellent intra-rater relative reliability (ICC = 0.86-0.98; 95% CI = [0.81-0.99]) was observed, with SEM values of 0.1-0.6 and MDC95 values of 0.3-1.7 points. Moderate to excellent video-based inter-rater reliability was found (ICC = 0.69-0.99; 95% CI [0.56-0.99]), with SEM values of 0.1-0.7 and MDC95 values of 0.3-2.0 points. Pairwise comparisons among raters showed moderate to excellent relative reliability (ICC = 0.57-0.99; 95% CI [0.35-0.99]), with SEM values of 0.1-0.5 and MDC95 values of 0.2-1.3 points. Conclusions: Subjective PR assessments performed using the INPP framework demonstrated good to excellent intra-rater relative reliability and moderate to excellent video-based inter-rater relative reliability, together with generally low absolute measurement error in elite youth football athletes. These findings provide preliminary psychometric support for the use of standardized PR assessments in research and applied sport settings.