Effectiveness of Neuromuscular Electrical Stimulation After Stroke

35 Hz Versus 50 Hz Frequency Stimulation Effects on Motor Recovery in Older Adults After Stroke. A Randomized Clinical Trial

A Randomized Clinical Trial (RCT) was conducted to determine the effects of two neuromuscular electrical stimulation protocols with different stimulation frequencies on motor recovery in older adults with spastic hemiparesis after a stroke.

Impairment of the upper limb is one of the most frequent consequences of stroke and directly impacts on the patient's functional status and quality of life. It is estimated that less than 50% of stroke survivors will recover arm function, which will exert a great economic, social and personal toll. Neuromuscular electrical stimulation (NMES) is one of the techniques suggested for upper limb recovery in stroke patients. However, after considering the bibliographic background, more studies are required in order to test its effectiveness, to establish the most efficient NMES protocols and to assess the characteristics of the patients who can benefit the most from this treatment. With this regard, the parameters of the stimulation are currently subject to debate, and more data are needed to optimize the application of this treatment. The aim of this study was to evaluate and compare the effects of two neuromuscular electrical stimulation protocols with different stimulation frequencies on motor impairment, kinaesthetic sensation, functional motor ability, activities of daily living, and quality of life in older adults with spastic hemiparesis suffering a stroke. To cope with the objective of the present study, RCT was conducted. Subjects who met inclusion criteria were recruited from a hospital rehabilitation unit. After the screening and signed consent, participants were randomly allocated to the control group or one of both experimental groups. NMES was applied on wrist and finger extensors for 30 minutes, 3 sessions per week for 8 weeks. The electrostimulation protocols were only differentiated in the parameter of the stimulation frequency, 35 Hz or 50 Hz, depending on the experimental group to which the patient belonged to. Outcome measures were collected at the beginning, after 4 and 8 weeks of treatment, and after a follow-up period (4 weeks).

Neuromuscular electrical stimulation (NMES) was applied on wrist and finger extensors for 30 minutes, 3 sessions per week for 8 weeks. The main electrostimulation parameters consisted of low-frequency current, a stimulation frequency of 50 Hz, symmetrical rectangular biphasic wave, and pulse duration of 300 μs.

Neuromuscular electrical stimulation (NMES) was applied on wrist and finger extensors for 30 minutes, 3 sessions per week for 8 weeks. The main electrostimulation parameters consisted of low-frequency current, a stimulation frequency of 35 Hz, symmetrical rectangular biphasic wave, and pulse duration of 300 μs.

A universal goniometer was used to measure the resting angle, active extension and passive extension of the wrist. A special JAMAR finger goniometer was used to evaluate the resting angle and active extension of the metacarpophalangeal joints of the fingers.

The grip strength was assessed by means of a JAMAR hydraulic hand dynamometer and the pinch strength using the JAMAR hydraulic pinch gauge. Unit of measurement was kgf. Three repetitions were done in both evaluations, taking the highest value and leaving a resting period of 1 minute between them.

Hypertonia of the finger and wrist flexors was measured using the modified Ashworth scale (MAS). MAS was used to categorize the severity of muscle tone by judging resistance to passive movement. It is a 6-point scale (0, 1, 1+ 2, 3, and 4) that ranges from 1 (=no increase in tone) to 4 (=limb rigid in flexion or extension). The assessment was started 5 minutes after laying the subject down in the supine position and using a single passive movement to evaluate each muscle group.

The Muscle Trainer model METR-0 (Mega Electronics Ltd, Kuopio, Finland) surface electromyograph was used. Circular adhesive surface bipolar electrodes (Ambú® Blue Sensor) were used and placed parallel to the muscle fibers. The mean amplitude of the EMG signal (in µV) of the muscle was recorded in the radial extensor and the radial flexor of the carpus. The patient was asked to perform maximum voluntary isometric contractions of both the flexors and extensors of the wrist for five seconds against manual resistance and the electrical activity of both the agonist and antagonist muscles was recorded simultaneously.

The Muscle Trainer model METR-0 (Mega Electronics Ltd, Kuopio, Finland) surface electromyograph was used. Circular adhesive surface bipolar electrodes (Ambú® Blue Sensor) were used and placed parallel to the muscle fibers. The peak amplitude of the EMG signal (in µV) of the muscle was recorded in the radial extensor and the radial flexor of the carpus. The patient was asked to perform maximum voluntary isometric contractions of both the flexors and extensors of the wrist for five seconds against manual resistance and the electrical activity of both the agonist and antagonist muscles was recorded simultaneously.

The Muscle Trainer model METR-0 (Mega Electronics Ltd, Kuopio, Finland) surface electromyograph was used. The antagonist co-activation ratio, both for the flexors and extensors of the wrist, was calculated using the following formula (antagonist activity/ [agonist activity + antagonist activity] x100%) (Reference: J Electromyogr Kinesiol. 2014;24:731-738) which provides an estimate of the relative activation of the agonist-antagonist muscle pair and also of the magnitude of the co-activation of the antagonist.

Hand kinaesthesia was assessed by the Revised Nottingham Sensory Assessment (RNSA) subscale. The RNSA includes three subscales: tactile sensation, kinesthetic sensation, and stereognosis. For kinesthetic sensation, all three aspects of the movement were tested: appreciation of movement, its direction, and accurate joint position sense. The limb on the affected side of the body was supported and moved by the examiner in various directions but the movement is only at one joint at a time. The patients were asked to mirror the change of movement with the other limb. This subscale ranges from 0 to 3. Higher scores indicate better kinaesthetic sensation.

A score of the Barthel Index ranging from 0 to 100 was collected where 0 is the minimum (worst outcome) and 100 is the maximum (best outcome).

COOP/WONCA charts were used. This instrument is a generic health status questionnaire which comprises nine single-item scales: physical fitness, feelings (mental well-being), daily activities, social activities, change in health and overall health, pain, social support, and quality of life. Each chart is rated on a five-point Likert scale with accompanying pictorial representations. Lower scores indicate better health-related quality of life.

Inclusion Criteria: Age ≥ 60 years Post-stroke spastic hemiparesis Mild-moderate hand impairment A score ≤ 3 on the modified Ashworth scale for wrist and finger flexors Active wrist extension ≥ 5º from the resting position Wrist extension response to stimulation Post-stroke period < 18 months Clinical stability Mini-Mental State Examination score ≥ 23 Exclusion Criteria: Previous hemiparesis due to stroke Dermatological reactions with the application of stimulation Significant sensory deficits in the affected arm Previous musculoskeletal problems of the hand Treatment with the botulin toxin Anti-spastic medication usage Cardiac pacemaker, implanted electronic device, or metal implants in the affected arm Complex regional pain syndrome Severe aphasia, history of epileptic seizures, psychiatric disorder or important alterations of behavior Severe visual impairment Any comorbid neurological disease Important deformity or obesity that affects the application of the NMES Potentially fatal cardiac arrhythmia or another decompensated heart disease Systemic infectious process, cancer or another terminal disease