Effect of TENS on Spasticity

Post-stroke spasticity is a common consequence of upper motor neuron lesions and is characterized by increased muscle overactivity and exaggerated stretch reflex responses. It can negatively affect motor function, daily activities, and quality of life in stroke survivors.

Transcutaneous electrical nerve stimulation (TENS) is a non-invasive and widely used rehabilitation modality that may modulate spinal and supraspinal neural mechanisms through activation of sensory afferent pathways. Although previous studies have reported potential benefits of TENS for spasticity management, findings remain inconsistent because of methodological heterogeneity, variability in stimulation parameters, and differences in individual treatment responses.

The purpose of this study is to evaluate the effects of sensory-level TENS on wrist flexor spasticity and spinal motor neuron excitability in individuals with chronic post-stroke spastic paresis. Specifically, the study will examine whether TENS influences clinical spasticity, the duration of any observed effects, the magnitude of treatment-related changes, and the reproducibility of these effects across participants.

Two complementary single-case experimental designs will be used. First, a withdrawal/reversal design (ABABA with washout periods) will be employed to evaluate the causal effects of TENS on outcome measures. Second, a nonconcurrent multiple-baseline design across participants will be used to assess the consistency of intervention effects across individuals.

TENS will be applied over the paretic wrist flexor muscles for 30 minutes using symmetrical biphasic rectangular pulses (100 Hz, 200 μs). Stimulation intensity will be adjusted to a clearly perceived sensory level without visible muscle contraction or discomfort.

The primary outcomes are clinical spasticity, assessed by muscle reaction angle during rapid passive stretch, and spinal motor neuron excitability, assessed by the Hmax/Mmax ratio obtained from flexor carpi radialis H-reflex recordings. Repeated measurements will be performed throughout the experimental phases to evaluate immediate and time-dependent changes associated with TENS application.

This study is expected to provide individual-level evidence regarding the effects and temporal characteristics of sensory-level TENS in chronic post-stroke spasticity.

Inclusion criteria

• Age between 18 and 70 years
• Post-stroke wrist flexor spasticity scored as Grade 2 or 3 on the Australian Spasticity Assessment Scale (ASAS), specifically selecting patients whose passive stretch resistance (post-catch response) can be easily overcome to ensure accurate and unconfounded electrophysiological evaluation.
• At least 6 months post-stroke (chronic phase).
• Provision of voluntary, written informed consent prior to study enrollment.

Exclusion criteria

• Age <18 or >70 year
• Contraindications to transcutaneous electrical nerve stimulation (e.g., implanted electronic devices, history of epilepsy, or localized skin lesions preventing electrode placement)
• Concomitant wrist contracture or pain sufficient to impede clinical evaluation
• Structural abnormalities of the elbow joint obstructing median nerve stimulation
• Median nerve neuropathy or injury in the affected upper extremity.
• Non-stable dosage of antispastic medications within the 2 weeks prior to baseline
• Initiation of medications affecting nerve conduction (e.g., antidepressants, anticonvulsants, anesthetics) within the past month; patients on a stable dose for >1 month remain eligible
• Botulinum toxin injection in the target spastic muscles within the preceding 3 months
• History of neurolytic procedures targeting spasticity in the affected limb.
• History of orthopedic or neurological surgery targeting spasticity in the affected limb
• Cognitive impairment severe enough to compromise adherence to study protocols
• Inability to maintain the required testing positions for the upper extremity joints (shoulder, elbow, forearm, and wrist)
• Pregnancy or breastfeeding
• Presence of active malignancy at or near the treatment area.