Transcutaneous Electrical Nerve Stimulation (TENS)

TENS involves the application of mild, pulsating currents to the cutaneous nerve fibers in the peripheral nervous system via one or more pairs of electrodes attached to the skin. The amplitude of current is typically adjusted across the sensory threshold to produce a comfortable, tingling sensation. TENS is used in the treatment of disorders related to the somatic and autonomic nervous systems (ANS) which are key components of the peripheral nervous system. The somatic nervous system is associated with the voluntary control of body movements via skeletal muscles. It consists of segments of nerves from the spinal cord and brain stem, where each segment contains afferent nerves and efferent nerves responsible for relaying sensation from the body to the Central Nervous System (CNS) and sending out commands from the CNS to the body to stimulate muscle contraction respectively. In neuromuscular disorders, disruptions in the afferent and efferent pathways lead to symptoms that may include loss of selective motor control, abnormal posture, exaggerated reflex responses, irregular muscle tone, loss of dexterity, muscle weakness and muscle atrophy.

The ANS works without a person’s conscious effort and regulates certain body functions such as blood pressure, heart rate, body temperature, digestion, metabolism, urination and defecation, sexual function and emotional response. The ANS is sub-divided into the sympathetic nervous system that promotes the “fight or flight” response and the parasympathetic nervous system that promotes the “rest and digest” response. These two divisions interact in an antagonistic fashion to modulate vital functions and achieve homeostasis in the ANS. When there are cellular and systemic disequilibrium in the ANS, it may lead to symptoms such as gastrointestinal discomforts, sleep disorders, constipation, urinary incontinence, tachycardia (fast heart rate), low blood pressure, severe anxiety or depression, faintness, fatigue and disturbing aches and pains.

TENS
in neuromuscular disorders

The application of TENS recruits massive diameter of cutaneous afferents to influence neural signaling in the affected muscles and nerves. For example, in the treatment of spasticity, the application of TENS on targeted muscles causes a suppression of alpha motoneuronal excitability that leads to the normalization of spinal cord hyperreflexia [13] and improvement of spasticity[11].

TENS
in pain relief

Pain relief using TENS is based on the gate-control theory of pain, which asserts that non-painful inputs shut the nerve gates from painful stimuli, thereby inhibiting painful sensations from being transmitted to the brain [14]. TENS may also modulate pain by causing an increase in the release of endogenous neurotransmitters such as opioids, serotonin, GABA and Glutamate during synaptic transmission [15].

TENS
in sleep disorders

In sleep studies, sleep deprivation has shown to increase sympathetic nervous system activity and is mirrored by an increase in blood pressure [16]. The application of the TENS can influence the vagal afferent pathways that are involved in the activation of the HPA axis which coordinates the adaptive responses to stressors [17], increasing parasympathetic supply to signals the body to relax and contribute to sleep improvements.

References:

[13] Liu Z, Dong S, Zhong S, Huang F, Zhang C, Zhou Y, Deng H. The effect of combined transcranial pulsed current stimulation and transcutaneous electrical nerve stimulation on lower limb spasticity in children with spastic cerebral palsy: a randomized and controlled clinical study. BMC Pediatr. 2021 Mar 24;21(1):141.

[14] Melzack R, Wall PD. Pain mechanisms: a new theory. Science. 1965 Nov 19 ;150(3699):971-9. doi: 10.1126/science.150.3699.971. PMID :5320816.

[15] Vance CG, Dailey DL, Rakel BA, Sluka KA. Using TENS for pain control: the state of the evidence. Pain Manag. 2014 May;4(3): 197-209.doi: 10.2217/pmt.14.13. PMID: 24953072; PMCID: PMC4186747.

[16] Gangwisch JE, Heymsfield SB, Boden-Albala B, Buijs RM, Kreier F, Pickering TG, Rundle AG, Zammit GK, Malaspina D. Short sleep duration as a risk factor for hypertension: analyses of the first National Health and Nutrition Examination Survey. Hypertension. 2006 May;47(5):833-9. doi: 10.1161/01.HYP.0000217362. 34748.e0. Epub 2006 Apr 3. PMID: 16585410.

[17] Tsigos C, Chrousos GP. Hypothalamic-pituitary-adrenal axis, neuroendocrine factors and stress. J Psychosom Res. 2002 Oct;53(4):865-71. doi: 10.1016/s0022-3999(02)00429-4. PMID: 12377295.

Transcutaneous Electrical Nerve Stimulation (TENS)