The TENS machine uses electrical pulses to stimulate sensory nerves, motor nerves and cell membranes
How TENS works
TENS is electrotherapy or electrical stimulation.
Depending on the purpose of the therapy, stimulation is applied to one (or more) of three different parts of the human body:
- Sensory nerves
- Cell membranes
- Motor nerves
"How TENS works" is best explained in terms of what is being stimulated and why.
Sensory nerves - the original TENS
TENS therapy relieves pain by stimulating the body's sensory nerve fibres to reduce pain related activity in the nervous system.
It works through two main mechanisms that help to alter and relieve the experience of pain:
- The first is a mechanism known as Pain Gating: pleasant signals travel along nerve fibres more quickly than painful signals; they reach the base of the brain first and block the painful signals from reaching the pain sensing areas of the higher brain
- Other sensory methods of pain relief that rely upon this mechanism include massage, acupressure, acupuncture, heat and cold packs or creams
- The second process is actually a group of mechanisms, that release natural, pain-inhibiting chemicals such as beta-endorphin
- Analgesic pharmaceuticals use manufactured chemicals (e.g. morphine) to achieve a similar outcome
However, the release of beta-endorphin is not toxic like manufactured chemicals and it also encourages a feeling of well-being - just like the "runner's high".
Sensory nerves send messages:
- pleasant sensations
- sharp pain
- dull pain
Pleasant signals travel faster than painful signals and reach the base of the brain first.
Cell Membrane Stimulation - ECS
An active human body will heal more quickly than an inactive body.
Inactivity slows the metabolism, inhibits healthy levels of cell membrane activity (opening of cell wall) and thus holds back injury recovery and healing times.
When you are forced to rest your body due to injury, surgery and associated pain, compromised electrical activity can be overcome by supplementing with externally applied electrical stimulation (ECS).
The benefits of cell membrane stimulation are associated with improved blood and lymphatic circulation, meaning:
- Removal of accumulated waste product such as dead cells, excess fluid and bruising - hastens the repair process
- Increased supply of oxygen, proteins and nutrients - needed for complete repair
- Breakdown of scar tissue or other unwanted fibrous tissue - reduces stiffness and improves mobility
When a cell is at rest, protein molecules and several other nutrient molecules cannot cross the membrane.
As a result, cell repair is compromised and slow.
Externally applied electrical stimulation addresses the problem. The time to heal the injury is halved, compared to no stimulation.
Motor nerve stimulation - EMS
Motor nerve stimulation is used to aid circulation, prevent muscle atrophy and re-condition muscles after injury or surgery. It is referred to as EMS - electrical muscle stimulation, (sometimes NMS for neuromuscular stimulation).
During periods of enforced inactivity (due to injury, illness or surgery), voluntary exercise is severely restricted. The dilemma is that there are many therapeutic benefits associated with regular exercise, without which healing can be slow or compromised and muscles can begin to waste or atrophy.
The dilemma is resolved with the use of electrical stimulation of motor nerves or muscle. The electrical signal is surged and the electrodes are placed over motor nerves or direct to the muscle.
A motor nerve stimulus of moderate intensity and high frequency activates the nerves supplying voluntary muscles, causing them to contract and release. as the stimulus surges ON and OFF. This is helpful in avoiding muscle atrophy and / or rebuilding muscle strength.
A motor nerve stimulus of lower frequency activates the smooth or involuntary muscle fibres, causing them to activate and release. This is helpful for improved circulation and smooth muscle condition.
In both cases, unused neural pathways can be re-activated, reinforced and, ultimately, returned to a healthy state. Muscle memory is therefore reinstated.
Motor nerves receive messages:
- from the brain, to activate voluntary muscle
- from the autonomic nervous system, to activate involuntary muscle
When the motor nerve is damaged, stimulation can be applied directly to muscle fibre.
When EMS is deliberately used to re-establish neural pathways, e.g. after a stroke, it is called Functional Electrical Stimulation (FES).