Title: Immediate effect of restricted ankle dorsiflexion on ground reaction force and trunk acceleration during walking
Abstract: Accelerometer is widely used for gait analysis. The gait parameters calculated from trunk acceleration describes the features of gait patterns and represents the whole body motion in walking. However, they cannot evaluate the gait pattern corresponding to gait cycle. The aim of this study was to investigate the validity of an accelerometer for gait analysis corresponding to the gait cycle in healthy subjects on restricted ankle joints, which simulated the characteristic motion of the elderly. Eight healthy volunteers walked with custom-made ankle braces under the following two conditions: walking without restricted ankle joint (free), and walking with restricted ankle dorsiflexion at 0° (restricted). The walking speed between two conditions was fixed on the same cadence, and tri-axis trunk acceleration on the third lumbar vertebrae and GRF from 4 force plates were measured. The peak of GRF (GRFmax) and its appearance time (GRFmax- t ) at mid stance to terminal stance were extracted from the vertical component of GRF on the right foot, the peak of acceleration during the identical phase in GRF (ACCmax), and the amplitude ratio of the autocorrelation function (ACF) were calculated from the vertical component of trunk acceleration. These kinematic parameters were compared between two conditions though the paired t -test ( P < 0.05). This study was approved by the Ethical Committee of Kawasaki University of Medical Welfare. GRFmax and the ACF were significantly smaller in the restricted condition compared to the free. GRFmax- t was significant earlier in restricted condition compared to the free. There was no significant difference between the ACCmax for the two conditions. This immediate effect shows that the restriction to ankle dorsiflexion changes the gait pattern represented in vertical GRF and trunk acceleration. This may suggest that these gait parameters can be used in the evaluation clinical risk such as frailty.