Participants are seeking to unleash the full therapeutic potential of a newly developed, customizable and potentially commericializable 10-channel Functional Electrical Stimulation (FES) to rehabilitate the gait of chronic stroke survivors. Patricipants will utilize the theory of muscle synergies from motor neurosciences, which are defined as neural modules of motor control that coordinate the spatiotemporal activation patterns of multiple muscles, to guide our personal selections of muscles for FES. Before applying FES stimulations to chronic stroke survivors, participants will have to define normal muscle synergies from age-matched healthy control participants (1 session for each participant). After comparing the difference in muscle synergies in both healthy subjects and chronic stroke survivors, participants are attempting to rehabilitate the gait of chronic stroke survivors by using the wearable. Each chronic stroke survivor will undergo 18-session FES training (~ 1 month).

It is hypothesized that FES will promote motor recovery by supplying the missing normal muscle synergies to chronic stroke survivors at their supposed times of activations in each step cycle during interventional training. It is also expected that the walk synergies of the paretic side of chronic stroke survivors should be more similar to healthy muscle synergies at the two post-training time points than before training. The healthy normal muscle synergies will be defined by EMG recordings from the recruited healthy participants.

Stroke is one of the leading causes of long-term adult disability worldwide. The impaired ability to walk post-stroke severely limits mobility and quality of life. Many recently-developed assistive technologies for gait rehabilitation are at present only marginally better at best than traditional therapies in their efficacies. There is an urgent need of novel, clinically viable, and effective gait rehabilitative strategies that can provide even better functional outcome for stroke survivors with diverse presentations.

Among the many new post-stroke interventions, functional electrical stimulation (FES) of muscles remains attractive. FES is a neural-rehabilitative technology that communicates control signals from an external device to the neuromuscular system. There is increasing recognition that rehabilitation paradigms should promote restitution of the patient's muscle coordination towards the normal pattern during training, and FES can achieve this goal when stimulations are applied to the set of muscles whose natural coordination is impaired. For this reason, FES is a very promising interventional strategy. Existing FES paradigms, however, have yielded ambiguous results in previous clinical trials, especially those for chronic survivors, likely because either stimulation were applied only to single or a few muscles, or the stimulation pattern did not mimic the natural muscle coordination pattern during gait. A multi-muscle FES, when applied to a larger functional set of muscles and driven by their natural coordination pattern, can guide muscle activations towards the normal pattern through neuroplasticity, thus restore impairment at the level of muscle-activation deficit.

The aim of our project is to rehabilitate the gait of chronic stroke survivors by delivering stimulations to multiple muscles, in their natural coordination pattern, using our wearable. participants will utilize the theory of muscle synergy from motor neuroscience to guide our personalizable selections of muscles for FES. Muscle synergies are hypothesized neural modules of motor control that coordinate the spatiotemporal activation patterns of multiple muscles. Our customizable FES pattern for each stroke survivor will be constructed based on the normal muscle synergies - identified from age-matched healthy subjects - that are absent in the stroke survivor's muscle pattern during walking. Since muscle synergies represent the natural motor-control units used by the nervous system, reinforcement of their activations through FES should lead to a restoration of normal neuromuscular coordination, thus more natural post-training gait.

Inclusion Criteria:

For chronic stroke survivors:

1. Right-handed elderly chronic stroke survivors; age ≥40; ≥6 months post-stroke
2. Unilateral ischemic brain lesions
3. Participants should be able to walk continuously for ≥15 min. with or without assistive aid

For healthy participants:

1. Healthy, right-handed subjects, age ≥40, free from any history of major neurological, musculoskeletal, and psychiatric disorders
2. Able to walk continuously for ≥20 min. without fatigue.

Exclusion Criteria:

For both healthy participants and chronic stroke survivors:

1. Cannot comprehend and follow instructions, or with a score <21 on the mini-mental state exam;
2. Have cardiac pacemaker;
3. Have skin lesions at the locations where FES or EMG electrodes may be attached;
4. Have major depression;
5. Present with severe neglect

Age-matched healthy control subjects will be recruited through advertisements. Chronic Stroke Survivors will be recruited from the local community such as clinic.