A hip test battery for clinical practice: reliability, normative data, and the pitfalls of Limb Symmetry Index

Background Reliable and clinically interpretable hip assessments are essential to guide evaluation, monitoring, and return-to-sport decision-making. However, no comprehensive test battery currently integrates intra- and inter-rater reliability, normative data in healthy individuals, and the reliability of the Limb Symmetry Index (LSI). Methods This cross-sectional reliability study included 94 healthy recreational adults (mean age 28.4 ± 8.5 years; 39% women). A subsample (n = 22) underwent a retest after 7 ± 2 days to assess intra-rater reliability. Outcome measures included hip range of motion (flexion, internal and external rotation), isometric hip strength (flexors, abductors, adductors), and functional performance tests (medial hop, single-leg squat, modified Star Excursion Balance Test [mSEBT], and endurance squat). The Limb Symmetry Index (LSI) was calculated for relevant outcomes. Reliability was assessed using intraclass correlation coefficients (ICC[2,1]), along with standard error of measurement (SEM) and minimal detectable change at the 95% confidence level (MDC95%). Results Most hip strength and range-of-motion measures demonstrated good reliability (ICC > 0.70), with MDC values of 55–79 N for strength and 15–18° for hip flexion. Medial hop performance showed excellent reliability (ICC = 0.89–0.95; MDC = 18–26 cm), and mSEBT demonstrated low measurement error (MDC = 9–14 cm). In contrast, single-leg squat and endurance squat tests showed lower reliability. Medial hop performance was moderately correlated with hip abductor (r = 0.52) and adductor strength (r = 0.51). LSI demonstrated poor reliability (ICC < 0.50; MDC ≈ 27%). Conclusions Range-of-motion measures, particularly active and passive hip flexion, demonstrated the highest levels of reliability. Strength tests showed good reliability but were associated with high measurement error, limiting their sensitivity to detect individual changes. Among functional tests, the medial hop demonstrated excellent reliability. In contrast, adductor-to-abductor strength ratios and the Limb Symmetry Index (LSI) showed poor reliability and high MDC values (≈ 27%), limiting their use as standalone decision-making criteria. These findings support the preferential use of absolute measures within a multidimensional assessment framework.