Reliability of Hop Distance and Frontal-Plane Dynamic Knee Valgus Angle during Single-leg Horizontal Hop Test

Context: Single-leg hop for distance (SHD) performance and twodimensional (2-D) video assessment of frontal-plane knee valgus, during the single-leg landings, have been reported to identify the risk of knee injuries such as patellofemoral pain syndrome and/ or anterior cruciate ligament tears. There are limited studies investigating the reliability and measurement error in single-leg hop for distance test and the 2-D video analysis of knee valgus angle on landing from this maximal forward hop. Objective: To evaluate the reliability and measurement error of hop distance and 2-D video assessment of lower limb frontal-plane dynamic knee valgus on landing during the SHD task. Design: Repeated measures reliability study. Participants: 12 recreationally active university students (8 men and 4 women 34.2 ± 3.1 y, height 170.8 ± 6.5 cm; mass 82.1 ± 15.9 kg). Main outcome measurement: Within and between-days reliability and measurement error values of hop performance and 2-D frontalplane projection angle (FPPA) during SHD test. Methods: For hop and 2-D tests: participants performed maximal SHD with standard 2-D digital video recording of the landing for assessment of FPPA. Results: For hop test distance: the within-day ICCs showed good to excellent reliability (0.89-0.93), and between-days ICCs were good, (0.85- 0.90). Standard error of measurement for SHD value ranged from 6.52- 9.83 cm. FPPA on landing: the within-day ICCs showed good reliability (0.87 to 0.90), and between-days ICCs were good, (0.81-0.88). Standard error of measurement for 2-D values ranged from 1.33-1.61°. Conclusions: Hop distance and 2-D FPPA on landing during SHD were shown to be a reliable measure of lower extremity performance and dynamic knee valgus. Using the measurement error values existing along with previously published normative data, clinicians can now make informed decisions about individual performance and variations in performance/injury risk following interventions.