Background Tissue response to repeated loading of the lateral ankle during arthrometer testing is unknown, and may be affected by number of trials and rate of loading.
Objective To determine tissue response changes from repeated anterior displacement testing in those with and without chronic ankle instability (CAI).
Setting Biomechanics laboratory.
Participants Of 53 volunteers; 36 recreationally active individuals participated (17 males, 19 females; age = 21.9 ± 2.7 years, body mass = 67.2 ± 12.5 kg, height = 168.8 ± 10.4 cm). Eighteen participants were designated as CAI and reported repeated sprains and Cumberland Ankle Instability Tool (CAIT) scores ≤24; 18 controls reported no ankle sprains with CAIT scores ≥ 28.
Interventions Three trials of anterior displacement to 150 N (LigMaster, version 1.26, Sport Tech, Inc., Charlottesville, VA, USA) were applied, then unloaded past 0 N until displacement was measured at 0 mm.
Main outcome measurements Displacement from 0 mm at 0 N during unloading and rate of unloading were determined for each trial. Repeated measures ANOVA and post-hoc comparisons were used to determine differences in unloading rates and displacement across 3 trials for each group and across all participants.
Results Rate of unloading was not significantly different across trials (p > 0.05), nor was displacement across 3 trials between controls (5.4 ± 4.2 mm) and CAI (6.0 ± 4.2 mm) individuals (p = 0.87, ηp 2 = 0.0). Across all participants, the displacement of trial 1 (6.7 ± 3.4 mm) was significantly greater than trial 3 (4.7 ± 2.5 mm, p = 0.001, ηp 2 = 0.17).
Conclusions The significant difference between trials 1 and 3, but not between successive trials, may indicate fluid removal from the ligament over repeated trials, allowing for the isolation of the collagen matrix. The influence of repeated loading and unloading should be considered in arthrometer assessment, as the number of trials explained only 17% of the variance. Further research is needed to determine the optimal number of pre-conditioning cycles for a stable tissue response.