title: Reliability of landing 3D motion analysis: implications for longitudinal analyses.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Cincinnati Children's Hospital Medical Center, Sports Medicine Biodynamics Center and Human Performance Laboratory, Cincinnati, OH 45229, USA. kevin.ford@cchmc.org
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Ford
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Myer
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Hewett
mesh_terms: D000293:Adolescent; D001265:Athletic Injuries / Q000453:epidemiology / Q000503:physiopathology; D001696:Biomechanical Phenomena; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009038:Motion; D015203:Reproducibility of Results; D014481:United States