Background and Aims: The accurate mechanisms of ankle instability cannot be assessed in the absence of
reliable knowledge about ground reaction force (GRF) variables. The purpose of this study was to evaluate
the test-retest reliability of GRF variables during forward and lateral jump-landing in volleyball players with
functional ankle instability (FAI).
Methods: Eighteen professional volleyball players with unilateral FAI participated in this study. They
performed four jump-landing trials in forward and lateral directions. After a one-week interval, the
repeatability of GRF variables including peak and time to peak of the three components of GRF (Fx, Fy, Fz)
were assessed using intraclass correlation coefficients (ICC), standard errors of measurement (SEM), and
coefficient of variation (CV).
Results: All variables in both forward and lateral jump-landing showed high to very high repeatability.
However, time to peak of Fx in lateral jump-landing demonstrated moderate repeatability (ICC = 0.67). The
CVs of all GRF measures were less than 10% except for the peak and time to peak of Fx component in
lateral jump-landing (14.55% and 13.15%, respectively). In general, the repeatability of GRF variables in
forward jump-landing was greater than that in lateral jump-landing.
Conclusion: GRF variables in forward and lateral jump-landing had high consistency. These parameters
were found to be useful in the assessment of GRF patterns in subjects with FAI.