But this isn't addressing the wrong signals causing spasticity which I consider the major failure of all eStim techniques.
The proper research on this would be a way
to stop the signals causing spasticity instead of this stupid; 'Hey,
let's try to overcome the spasticity, which doesn't get you recovered at
all!' 'Does anyone in stroke have any brains at all?'
Therapeutic and orthotic effects of an adaptive functional electrical stimulation system on gait biomechanics in participants with stroke
Journal of NeuroEngineering and Rehabilitation volume 22, Article number: 62 (2025)
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.
Background
Stroke is an acute cerebrovascular disease with a high mortality and disability rate, which poses a severe threat to human life and health [1]. Hemiplegic gait is a common sequela characterized by weakness or spasticity in the affected limb and a loss of muscle control [2]. At the ankle level, the most common manifestations of the injury are lack of foot clearance during the swing and reduced forward propulsion during late stance [3]. Furthermore, the damage to the ankle muscles can result in compensatory actions involving other parts of the body [4]. For instance, individuals may lean on the unaffected limb to maintain balance and facilitate forward movement [5]. These disturbances can decrease walking speed and stability, induce asymmetric gait, and elevate the risk of falls [6, 7]. Consequently, identifying appropriate intervention methods to correct and treat hemiplegic gait is vital.
Functional Electrical Stimulation (FES) is a common intervention technique to correct hemiplegic gait, which transmits control signals from external devices to the neuromuscular system to activate muscles [8]. In 1961, Liberson et al. first applied FES to increase dorsiflexion angle during the swing phase in participants with stroke [9]. Since then, numerous FES systems have been developed to assist participants with stroke by correcting foot drop [10], enhancing push-off at the terminal stance phase [11], and improving knee [12] or hip control [13]. To address the highly nonlinear and time-varying nature of the stimulated muscle, researchers have developed several closed-loop control strategies, including finite state machines [14], artificial neural networks [15], fuzzy logic [16], and Iterative Learning Control (ILC) [10]. Among these, ILC has gained widespread application due to its ability to improve system performance through repeated trials by learning from previous iterations [17]. In ILC, control inputs are updated based on the error between the actual output and the desired output from the previous iteration, enabling the system to progressively reduce errors with each cycle. Building on this iterative learning process, ILC offers fast convergence, stable tracking performance, and robustness to external disturbances, making it particularly effective for optimizing neuromuscular control. However, most of these studies concentrate on the immediate orthotic effects of FES, neglecting the neuromuscular system’s capacity for enduring adaptation. Long-term use of FES can result in physiological changes, which may also affect motor performance in the absence of FES usage, and this carry-over effect is frequently termed the therapeutic effect [18]. Some studies recruited groups of participants with chronic stroke for more than four weeks of FES training, consistently observing improvements in gait performance [19,20,21]. FES has also been found to be an effective alternative to ankle foot orthosis for treating foot drop after stroke in other studies [22, 23]. Nonetheless, these studies often used basic open-loop FES systems with preset and fixed stimulus parameters, including pulse frequency, width, and current amplitude. These parameters cannot be dynamically adjusted to accommodate the physiological changes in participants with stroke after daily training, thus hindering the attainment of the optimal therapeutic effect. This makes the exploration of long-term training under closed-loop FES a worthwhile endeavor.
The effectiveness of FES systems in a clinical context can be assessed by analyzing various gait parameters. Regarding orthotic effects, researchers found that FES helped increase walking speed [24], reduce energy expenditure [25], increase knee-ankle angle [26], and change spatiotemporal characteristics [27]. In terms of therapeutic effects, many studies have demonstrated the effectiveness of FES in improving gait speed [20, 28]. FES also exhibited a positive therapeutic effect on additional activity-related parameters, including walking independence [19], walking distance [22], physiological cost index [20], and other variables. In addition to the above gait functions, after six weeks of FES training, Kesar et al. [21] found an improvement in gait biomechanics, including paretic propulsion and swing phase knee flexion. However, most of these studies focused on rehabilitating the affected limb to match the capabilities of non-disabled individuals, overlooking gait asymmetry caused by limb compensation. Center of pressure (COP) represents the cumulative neuromuscular response that controls the movement of the center of mass and is often utilized to evaluate balance control, gait deficits, and orthotic effect [29,30,31]. During the stance phase, the anteroposterior (AP) COP trajectory provides specific information that governs the forward progression of the center of mass. The medial-lateral (ML) COP movement mainly reflects the control process for regulating lateral stability during the single stance phase and the ability to shift weight between limbs during the double stance phase [29]. Nolan et al. [31] and Francis et al. [32] found that stimulating muscles like the tibialis anterior (TA) and gastrocnemius (GAS) could promote the anteroposterior movement of the center of pressure. Bamber et al. observed that stimulation of the peroneus longus muscle improved the lateral center of pressure during the stance phase [33]. Although applying functional electrical stimulation to ankle joint muscles can improve the center of pressure in previous studies, few of them considered the changes in symmetry after FES intervention.
In the previous research, we developed a hybrid adaptive functional electrical stimulation system [11]. Building upon this foundation, this study conducted extended evaluations. The orthotic effect of FES on COP symmetry, which is important for maintaining balance control while walking, was examined. Moreover, the therapeutic effect of the adaptive FES was studied by assessing improvements in gait biomechanics. We hypothesize that activating specific muscles in participants with stroke can facilitate the movement of the center of pressure on the hemiplegic side, improving gait symmetry. Furthermore, prolonged FES training might induce muscle strength and nerve excitability alterations, ultimately achieving therapeutic benefits.
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