Bilateral hip exoskeleton assistance enables faster walking in individuals with chronic stroke-related gait impairments

Abstract

Millions of individuals surviving a stroke have lifelong gait impairments that reduce their personal independence and quality of life. Reduced walking speed is one of the major problems limiting community mobility and reintegration. Previous studies have shown positive effect of robot-assisted gait training utilizing hip exoskeletons for individuals with gait impairments due to a stroke, leading to increased walking speed in post-treatment compared to pre-treatment assessments. However, no evidence emerged of a significant increasing in walking speed attributable to device usage compared to walking without the device. In this pilot investigation, we observed that hip flexion/extension assistance delivered by a portable bilateral powered hip exoskeleton increased overground self-selected walking speed by 20.2 ± 5.0% on average among six chronic post-stroke survivors. When comparing walking with and without the hip exoskeleton within the same experimental session, the observed speed increment resulted in statistically and clinically meaningful improvement (0.14 ± 0.03 m/s > minimal clinically important difference, p = 0.015). The increased walking speed was the result of a higher self-selected cadence and longer step length both on the paretic and nonparetic limbs. By facilitating gait, a bilateral hip exoskeleton could be a viable technology for extending locomotor mobility and facilitating gait training of individuals affected by post-stroke hemiparesis.

Fig. 1

Self-selected walking speed measured during 10mWTs with and without the APO. On the left, colored bars represent the self-selected comfortable walking speed (m/s) measured during the 10mWTs in the following experimental conditions: (i) without the APO at the beginning and at the end of the session (NoAPO_baseline and NoAPO_final, grey), (ii) with the APO in assistive mode (AM, blue), (iii) with the APO in transparent mode (TM, bordeaux). The minimal clinically important difference (MCID) is indicated with dashed horizontal lines. On the right, colored bars represent the percentage change in the self-selected walking speed with respect to NoAPO_baseline. Aggregated data across participants are reported as means and standard error means. Colored dots represent individual study participants. The square brackets with the asterix indicate the statistically significant differences when comparing APO in AM versus NoAPO_baseline and APO in TM (post-hoc test p < 0.05).

Fig. 2

Changes in spatiotemporal parameters measured during the 10mWTs with and without the APO. Colored bars represent the variation in the spatiotemporal parameters in different walking conditions, compared to walking without the APO at the beginning of the session (NoAPO_baseline). Walking conditions are the following: walking with the APO providing assistance (AM, blue), with the APO in transparent mode (TM, bordeaux) and without APO at the end of the sesison (NoAPO_final, grey). From left to right, spatiotemporal parameters are cadence (steps/min), stride length (cm), paretic step length (cm), nonparetic step length (cm). Aggregated data are reported as means and standard errors. Colored dots represent individual study participants. The asterix indicate the statistically significant differences when comparing to NoAPO_baseline (post-hoc test p < 0.05).

Fig. 3

Hip angle, torque, and power measured during the 10mWTs with the APO in assistive mode. (a) The hip angle measured by APO encoders, the APO hip torque and power normalized to body mass. The angle, torque, and power profiles are shown for each participant; each profile is depicted by the average (solid line) and standard deviation (shadow area) over all the strides of the 10mWT in AM. (b) APO energy injected during the entire stride duration, normalized to body mass. All bar plots represent means and standard deviations computed over all the strides of the 10mWTs in AM for each participant. On the right, the averaged values across participants (Avg) for paretic (grey) and nonparetic side (black), that resulted statistically different (paired-ttest, p < 0.05).

Fig. 4

Lower-limb kinematics during treadmill walking with and without the APO. a, b) Hip, knee and ankle angle profiles of the paretic (a) and nonparetic limbs (b) during treadmill walking in the following conditions: (i) walking without the APO (NoAPO, grey), (ii) walking with the APO in assistive mode (AM, blue), (iii) walking with the APO in transparent mode (TM, bordeaux). Aggregated profiles across participants are shown as mean (solid line) ± s.e.m. (shadow area). c) Sagittal range of motion (ROM) of the hip, knee, and ankle joints of the paretic (left) and nonparetic (right) side. Aggregated data are reported in bar plots as mean ± s.e.m (n = 6) for the different walking conditions (NoAPO, AM, TM). Colored dots represent individual study participants. The percentage changes in AM with respect to NoAPO and TM are indicated above the bar plots. The asterix indicate the statistically significant differences when comparing APO in AM versus NoAPO_baseline (post-hoc test p < 0.05).

Fig. 5

Schematic of the experimental protocol and setup. The experimental protocol consisted of 5 sessions. The first session (Enrollment) included the evaluation of the study participants’ eligibility and a gait analysis overground without the APO. The second (Tuning) and the third (Familiarization) session were devoted to the tuning of the APO assistive profile and the familiarization with the exoskeleton assistance. Following these sessions, participants performed two Test sessions: one overground (OVG, day 4) and one on the treadmill (TRM, day 5). The OVG test session included 10mWTs under three different walking conditions: (i) without the APO at the beginning and at the end of the session (NoAPO_baseline, NoAPO_final, grey), (ii) with the APO in transparent mode (TM, bordeaux), (iii) with the APO in assistive mode (AM, blue). During the TRM test session, participants gait performance under the same three different conditions (NoAPO, TM, AM, circle) was assessed through gait analysis tests. On the right, a representative picture of the APO.