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