Abstract
BackgroundA contralateral pelvic drop, a transverse rotation and a lateral translation of the pelvis are essential features of normal human gait. These motions are often restricted in robot-assisted gait devices. The optional FreeD module of the driven gait orthosis Lokomat (Hocoma AG, Switzerland) incorporates guided lateral translation and transverse rotation of the pelvis. It consequently should support weight shifting during walking. This study aimed to investigate the influence of the FreeD module on trunk kinematics and hip and trunk muscle activity.MethodsThirty- one healthy adults participated. A video analysis of their trunk movements was performed to investigate the lateral chest and pelvis displacement within the Lokomat (with and without FreeD), and this was compared to treadmill walking. Furthermore, surface electromyography (sEMG) signals from eight muscles were collected during walking in the Lokomat (with and without FreeD), on the treadmill, and overground. To compare the similarity of the sEMG patterns, Spearman’s correlation analyses were applied.ResultsWalking with FreeD elicited a significantly higher lateral pelvis displacement and a lower lateral chest displacement (relative to the pelvis) compared to walking with a fixated pelvis. No significant differences in the sEMG patterns were found for the Lokomat conditions (with and without FreeD) when comparing it to treadmill or overground walking.ConclusionsThe differences in pelvis displacement act as a proof of concept of the FreeD module. The reduction of relative lateral chest movement corresponds to a decrease in compensatory trunk movements and has its origin in allowing weight shifting through the FreeD module. Both Lokomat conditions showed very similar muscle activity patterns of the trunk and hip compared to overground and treadmill walking. This indicates that the Lokomat allows a physiological muscle activity of the trunk and hip during gait.
Highlights
A contralateral pelvic drop, a transverse rotation and a lateral translation of the pelvis are essential features of normal human gait
We started with the Lokomat conditions for two reasons: First, it was necessary because of the electrodes placement (EMG transmitter boxes cannot be placed under the leg cuffs) and secondly, the walking speed selected in the Lokomat was subsequently adopted for the treadmill and the overground condition
That significantly decreased to 2.27 cm (IQR = 1.80) in the Lokomat FreeD condition (p < 0.001, effect size = 0.95) The relative chest range of motion (ROM) of treadmill walking had a median of − 2.35 cm (IQR = 1.20), and it is negative since the maximal hip marker excursion was generally larger than the chest marker excursion
Summary
A contralateral pelvic drop, a transverse rotation and a lateral translation of the pelvis are essential features of normal human gait. The lateral translation of the pelvis intends to shift the center of gravity over the standing leg which involves a natural valgus position of the knee and relative hip adduction during the stance phase [2] These movements can be restricted by deformity, muscle weakness, impaired control and pain which further leads to an abnormality of the gait pattern [2]. This mechanism allows the legs to follow the lateral pelvic displacement and enables a natural valgus angle at the knee during the stance phase and a weight shift to the standing leg With this mechanism and because the patient in the FreeD is not so rigidly fixed compared to the conventional Lokomat, the manufacturer advertises that the patient can participate more actively in the lateral translation and transverse rotation. It should be possible to train balance skills which are often affected in patients with neurological disorders [3]
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