Reliability of landing 3D motion analysis: implications for longitudinal analyses.

PURPOSE: Biomechanical measures quantified during dynamic tasks with coupled epidemiological data in longitudinal experimental designs may be useful to determine which mechanisms underlie injury risk in young athletes. A key component is the ability to reliably measure biomechanical variables between testing sessions. The purpose was to determine the reliability of three-dimensional (3D) lower-extremity kinematic and kinetic variables during landing in young athletes measured within a session and between two sessions 7 wk apart.
METHODS: Lower-extremity kinetics and kinematics were quantified during a drop vertical jump. Coefficient of multiple correlations (CMC), intraclass correlation coefficients (ICC (3, k), ICC (3, 1)), and typical error (TE) analyses were used to examine within- and between-session reliability.
RESULTS: There were no differences in within-session reliability for peak angular rotations between planes with all discrete variables combined (sagittal ICC > or = 0.933, frontal ICC > or = 0.955, transverse ICC > or = 0.934). Similarly, the between-session reliability of kinematic measures were not different between the three planes of motion but were lower than the within-session ICC. The within- and between-session reliability of discrete joint moment variables were excellent for all sagittal (within ICC > or = 0.925, between ICC > or = 0.800) and frontal plane moment measures (within ICC > or = 0.778, between ICC > or = 0.748). CMC analysis revealed similar averaged within-session (CMC = 0.830 +/- 0.119) and between-session (CMC = 0.823 +/- 0.124) waveform comparisons.
CONCLUSION: The majority of the kinematic and kinetic variables in young athletes during landing have excellent to good reliability. The ability to reliably quantify lower-extremity biomechanical variables of young athletes during dynamic tasks over extended intervals may aid in identifying potential mechanisms related to injury risk factors.