The FreeD module for the Lokomat facilitates a physiological movement pattern in healthy people - a proof of concept study

Abstract

Background: A 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.

Methods: Thirty- 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.

Results: Walking 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.

Conclusions: The 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.

Keywords: Chest; Lateral translation; Path control; Pelvis; Rehabilitation; Robot-assisted gait therapy; Surface electromyography; Transverse rotation; Trunk movements; Weight shifting.

Conflict of interest statement

Ethics approval and consent to participate

Since the project did not fall under the Human Research Act, a “declaration of no objection/independence” was issued by the Ethics Committee of the Canton Zurich (Reference number BASEC Req-2017-00346). All participants were ≥ 18 years and gave written informed consent to participate.

Consent for publication

All authors have approved the manuscript for submission. All participants gave written informed consent to publish these data. No individual details, images or videos are included in the manuscript.

Competing interests

The authors declare that they have no competing interests and there are no financial competing interests to declare in relation to this manuscript.

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Figures

Fig. 1

Possible pelvis movements (a combination of lateral translation and transverse rotation) of the Lokomat FreeD module (Image courtesy Hocoma AG, Volketswil, Switzerland)

Fig. 2

The study procedure presents the four walking conditions (Lokomat FreeD, Lokomat Control, treadmill, overground). The measurements started with the Lokomat conditions in randomized order, followed by the treadmill condition and ended with the overground condition. To compare the similarity of the sEMG patterns across the conditions, Spearman’s correlation coefficients were calculated for each participant separately which led to the new variables ρFT, ρFO, ρCT, ρCO

Fig. 3

Overview of all averaged sEMG activity normalized to the mean amplitude of Lokomat and treadmill walking. The grey line at 60% of the gait cycle indicates the normalized toe-off. The 95% confidence interval is shown by colored areas. Mean walking speed for all conditions was 3.0 km/h

Fig. 4

Mean lateral displacement of the chest and pelvic marker for one stride over time from a bird’s eye view (upper panel, Control in green, FreeD in orange, and Treadmill in blue, average of 20 strides). To the right of those graphs, the according upper body movement is depicted. The lower panel shows the median lateral range of motion (peak-to-peak displacement) of the pelvic marker of each subject. Thereby, the grey vertical lines indicate the median values of the group

Fig. 5

Spearman’s correlation coefficients between muscle activity patterns of all eight muscles for all walking conditions. The y-axes of the bar charts show the size of the Spearman correlation coefficient and the x-axes show the single muscles. Abbreviations: ES = M.erector spinae, RA = M.rectus abdominis, OEA = M.obliquus ext.abdominis, GMe = M.gluteus medius, GMa = M.gluteus maximus, TFL = M.tensor fascia latae, AD = Adductors, VM = M.vastus medialis