Discordance Between Self-Reported Physical Activity and Field-Assessed Functional Capacity Among University Students: An Agreement and Directional Discordance Analysis

Background/Objectives: Self-reported physical activity is widely used in non-communicable disease (NCD) surveillance, yet its individual-level agreement with field-based markers of cardiorespiratory fitness remains poorly characterised in Gulf Cooperation Council (GCC) populations. This study examined the association, agreement, and directional discordance between self-reported physical activity (IPAQ Short Form, IPAQ-SF) and field-assessed functional capacity (Incremental Shuttle Walk Test, ISWT) among university students in Kuwait. Methods: In 389 students (76.3% female; mean age 20.2 ± 2.3 years) in Kuwait, IPAQ-SF activity was classified as low, moderate, or high and ISWT distance into sample-derived tertiles. Spearman correlations, Kruskal–Wallis tests with Dunn pairwise comparisons, cross-tabulation, and unweighted, linear-weighted, and quadratic-weighted Cohen’s kappa were used. Results: IPAQ activity showed a weak but significant correlation with ISWT distance (ρ = 0.209, p < 0.001). ISWT performance did not differ between the low- and moderate-IPAQ categories (Bonferroni-adjusted Dunn p = 0.162). Agreement was slight across all kappa estimates (unweighted κ = 0.083; linear-weighted κ = 0.137; quadratic-weighted κ = 0.192), with matching category assignment in only 38.8% of participants; lower-than-tertile IPAQ classification occurred in 42.9% and higher-than-tertile in 18.3%. Directional discordance differed significantly by sex (p < 0.001). A rank-based partial correlation adjusting for BMI, age, and sex was attenuated but remained significant (r = 0.144, p = 0.004). Conclusions: IPAQ-SF categories showed poor individual-level agreement with sample-derived ISWT functional-capacity tertiles among university students in Kuwait. Self-reported physical activity and field-based functional capacity should therefore be interpreted as complementary rather than interchangeable measures. Larger multi-university studies across the GCC are needed to confirm these findings.