Restricted Unilateral Ankle Dorsiflexion Movement Increases Interlimb Vertical Force Asymmetries in Bilateral Bodyweight Squatting

The purpose of this study was to investigate the effect of unilateral restrictions in ankle-dorsiflexion range of motion (DF-ROM) on interlimb vertical ground reaction force (vGRF) asymmetries. Twenty healthy and physically active volunteers (age 23 ± 3 years; height 1.72 ± 0.1 m; mass 74.9 ± 20.3 kg) performed 3 barefoot bodyweight squats (control condition) and with a 10° custom-built forefoot wedge under the right foot to artificially imitate ankle DF-ROM restriction (wedge condition). Force data were used to calculate the mean asymmetry index score for the upper descent phase, lower descent phase, lower ascent phase, and upper ascent phase during the bilateral squat. Significant differences were found for comparisons for each phase between conditions, with effect sizes ranging between 0.7 and 1.1. Asymmetry index scores indicated that for all phases, the unrestricted limb in the wedge condition produced greater vGRF. Therefore, interlimb differences in ankle DF-ROM can cause interlimb asymmetries in vGRF during bilateral squatting. As such, athletes with asymmetrical squat mechanics should be screened for interlimb differences in ankle DF-ROM to ascertain whether it is a contributing factor.