Therapeutic and orthotic effects of an adaptive functional electrical stimulation system on gait biomechanics in participants with stroke

Abstract

Background: In recent years, functional electrical stimulation (FES) has become a common intervention for stroke survivors to correct foot drop and improve gait biomechanics. While the orthotic effects of adaptive FES systems were well-documented, the center of pressure (COP) symmetry has been largely neglected. Furthermore, the long-term therapeutic effects of adaptive FES systems on gait biomechanics have received less attention. METHODS : This study applied a timing- and intensity-adaptive functional electrical stimulation system for evaluation and training tests to address these limitations. In the evaluation test, eight participants with chronic stroke walked under three FES conditions: no stimulation (NS), adaptive FES to the tibialis anterior (SA-ILC SCS), and hybrid adaptive FES to the tibialis anterior and the gastrocnemius (SA-ILC DCS). Nine healthy subjects walked under the NS condition as the control group. In the training test, two participants with stroke took part in a 21-day training session under the SA-ILC DCS condition.

Results: The results showed that the COP symmetry of participants with stroke in the SA-ILC SCS condition tended to improve compared to the NS condition, while the SA-ILC DCS condition showed significant improvement, approaching that of healthy subjects. After the 21-day treatment period, there was a tendency for improvement in the knee-ankle angle, anterior ground reaction force, and COP symmetry of both participants with stroke without assistance.

Conclusion: The observed improvements can be attributed to the hybrid adaptive FES targeting the tibialis anterior and gastrocnemius muscles. This study demonstrates that the adaptive FES system offers promising walking assistance capabilities and significant clinical therapeutic potential.

Trial registration: Ethics Committee of Zhujiang Hospital, Southern Medical University, 2022-KY-149-01. Registered 29 September 2022.

Keywords: Center of pressure; Functional electrical stimulation; Gait symmetry; Hemiplegic gait; Orthotic effect; Stroke; Therapeutic effect.

Fig. 1

The structure diagram of the adaptive FES system. The arrows indicate the positive directions of the three-dimensional force sensors, while $S_i$ ($i=1,2,3,4$) represents the i-th sensor

Fig. 2

Scheme of the training test

Fig. 3

Calculation method for COP parameters (left-side hemiplegia). The gray solid line represents the COP trajectory, with vertical segments indicating the single-support phase and diagonal segments representing the double-support phase. In the left panel, the red arrow shows the COP width on the paretic side, defined as the horizontal distance from the COP trajectory intersection to the midpoint of two consecutive gait events (toe-off to heel-strike of the same foot). The blue arrow indicates the COP width on the non-paretic side. In the right panel, the red arrow shows the COP length on the paretic side, defined as the vertical distance between two consecutive gait events (heel-strike to toe-off of the opposite foot). The blue arrow represents the COP length on the non-paretic side. LHS left heel-strike, LTO left toe-off; RHS: right heel-strike, RTO right toe-off, LSSP single-support phase of the left leg, RSSP single-support phase of the right leg

Fig. 4

Center of pressure trajectories for participants with stroke 3 (A), 4 (B), and 6 (C) under three FES conditions, compared with the healthy control (HCG)

Fig. 5

Box plot of (A) lateral symmetry and (B) anteroposterior symmetry at different FES conditions. HCG healthy control group. Significant difference: *P <0.05, **P <0.01, ***P <0.001

Fig. 6

Therapeutic effects from pre-training to post-training without FES: ankle angles (mean ± SD) for subject 1 (A) and subject 2 (E), knee angles (mean ± SD) for subject 1 (B) and subject 2 (F), anterior ground reaction force (mean ± SD) for subject 1 (C) and subject 2 (G), center of pressure (mean) for subject 1 (D) and subject 2 (H)

Fig. 7

Changes in gait parameters (mean ± SD) from pre-training to post-training without FES: A maximum ankle dorsiflexion angle during swing phase, B peak ankle plantarflexion angle, C maximum knee flexion angle, D peak AGRF, E lateral symmetry, and F anteroposterior symmetry. *denotes significant improvement in gait parameters at each training stage compared to pre-training. Significant difference: *P <0.05, **P <0.01, ***$P<0.001$