TENS and NMES Explained
You may have heard of TENS or NMES in human medicine or they may have been used on your animal's, but do you know what they are and how they work? This blog is here to answer those questions!
What are they?
Transcutaneous Electrical Nerve Stimulation (TENS) and Neuromuscular Electrical Stimulation (NMES), are both forms of electrotherapy that target our nerves via a mild electrical current. The primary purpose of TENS is to provide pain relief, whereas NMES is used to treat muscular weakness.
The machine which delivers the electrical current is a small battery-operated device, with sticky pads called electrodes that are placed on the treatment area. When the machine is on, the impulses pass through the electrodes into the body, causing a tingling sensation or contraction.
What are they used for?
TENS has a range of uses to reduce varying types of pain. In animals, it is most commonly used for chronic or long-term pain such as joint pain, pain related to osteoarthritis, or muscular pain, particularly in the back.
NMES assists in building and strengthening muscle, especially in cases where the animal has lost a significant amount. This loss of muscle is known as muscle atrophy, and can be caused by multiple things;
- Spinal or neurological injury where the limb loses function
- General disuse of a limb if the animal is in pain or recovering from surgery
- Crate rest following injury/surgery
- Gait compensation where the muscle is not used correctly so weakens over time
- Ageing, dogs with reduced activity and potentially osteoarthritic changes
In most cases, when I see an animal for rehabilitation they have some degree of muscle atrophy, which is why I prescribe exercises - NMES works best when combined with physical activity.
How do they work?
TENS works by stimulating the sensory nerves in the body to cause natural pain-relieving mechanisms to kick into action. The first of these mechanisms is the Pain Gate Theory. When the TENS is applied, sensory nerve fibres are stimulated so the nerves which normally transmit pain are overridden. This closes the pain gate so the transmission of pain signals is reduced. This method works at higher frequencies which aren’t always well tolerated by animals.
So the alternative is the Opioid Mechanism, with the TENS at a lower frequency, a substance called encephalin is released in the spinal cord. This substance reacts with receptors on the outer layer of our cells, and blocks them, meaning that painful signals are no longer sent to the brain. This is the most common method that TENS works by to relieve pain in our animals.
NMES simply works by sending electrical impulses that artificially activate the muscles causing them to contract and relax as if they were working. This starts the process of muscle re-education, essentially teaching the muscle to work again, which is why it is commonly used in dogs with spinal injuries who cannot walk unassisted.
NMES stimulates the muscle in the opposite order to normal muscle contractions, which can make it very tiring. This is why it is only applied for short periods, with plenty of rest for the muscle to recover.
In this video you can see NMES in action to target hindlimb weakness.
Do they work?
As is the case with lots of electrotherapies, they are not well researched in the veterinary world, but the research that is out there shows promising results.
TENS has been trialled in dogs with osteoarthritic pain in the knee joint (Johnston et al., 2002). The results showed pain levels improved as the dogs were able to bear more weight in the limb 30 minutes after therapy. This benefit lasted for a few hours afterwards, but additional pain management would be needed for the longer term.
In another study, TENS was applied to dogs with spinal arthritis over a course of 10 days (Krstic et al., 2010). All dogs that received the therapy had a significant decrease in pain at rest, during activity, and when touched. In this trial the TENS was applied daily, as TENS machines are relatively cost effective owners are able to purchase and use on their animals under the guidance of a therapist.
The research into NMES found that dogs recovering from surgery for cruciate ligament rupture, were significantly less lame, and had an increased thigh muscle circumference when the electrotherapy was used (Johnson et al., 1997). As previously mentioned, this electrotherapy works best alongside exercises, so it cannot be solely relied on to build muscle.
I am able to offer NMES and TENS if I think it is suitable for your animal's case. The machines can also be used by owners under my guidance, if the therapy needs to be applied daily. Please contact me if you would like advice on this or if you have any other questions - Nancy.
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Johnson, J.M., Johnson, A.L., Pijanowski, G.J., Kneller, S.K., Schaeffer, D.J., Eurell, J.A., Smith, C.W. and Swan, K.S. (1997) 'Rehabilitation of dogs with surgically treated cranial cruciate ligament-deficient stifles by use of electrical stimulation of muscles'. American Journal of Veterinary Research, 58, 1473-1478.
Johnston, K.D., Levine, D., Price, M.N. et al. (2002) 'The effect of TENS on osteoarthritic pain in the stifle of dogs'. Proceedings 2nd International Symposium on Physical Therapy and Rehabilitation in Veterinary Medicine.
Krstic, N., Lazarevic-Macanovic, M., Prokic, B. et al., (2010) 'Testing the effect of different electrotherapeutic procedures in the treatment of canine ankylosing spondylitis'. Acta Vet Brno, 60.