How to Use a Tens Unit to Tone Muscles

Electromyostimulation (EMS) helps world-class athletes enhance their sports performance and tone muscle faster. However, using a transcutaneous electrical nerve stimulation (TENS) unit for toning abs or other muscles won't work as it relieves pain by stimulating the nerves without building muscle.

Electromyostimulation (EMS) helps world-class athletes enhance their sports performance and tone muscle faster. (Image: Bogdanhoda/iStock/GettyImages)

Why TENS Doesn't Tone

Although TENS units use electrical impulses, they don't stimulate the correct neurons for muscle contraction. They stimulate sensory neurons that send pain signals to the brain, confusing and negating the pain signals, according to the Original TENS Units. They also promote the release of endorphins, which may help eliminate muscle pain.

Sensory neurons are just one of three types of neurons in the body. Your brain and spinal cord send signals to the body using interneurons that run through them that facilitate communication neuron-to-neuron, according to a 2011 thesis by cyclist and 2015 NATS North American Trials Championships winner Jeffrey C. Anderson for the School of Engineering Science at Simon Fraser University.

The spinal interneurons communicate with the motor neurons involved in muscular contraction. This is how you consciously make muscle movements when working out, unconsciously keep your balance or jump back in involuntary reaction to an unexpected stimulus.

EMS targets motor neurons directly, bypassing the interneurons completely. That means it can deliver longer and more contractions per minute than you would be able to consciously perform. More and longer contractions of the muscle fiber builds the muscle tissue faster than through a traditional workout.

Using TENS to Work Out

Although TENS units won't directly tone your muscles, using one can indirectly promote more rapid muscle growth. According to the manufacturer, the pulse sent won't fully contract your muscle, but it can help relax knots and relieve muscle pain. This may help improve your workout performance and thus tone your muscles faster.

For example, if you suffer from knee pain or stiffness when you work out, a portable TENS unit can help block the pain signals to your brain while stimulating endorphins that will make the exercise seem more pleasurable — or, at least less painful. Strap a mobile unit to your body and position the electrodes above, below and to each side of the knee cap.

For chronic shoulder pain, the pads should be positioned on the front and back of the shoulder joint and the front and back of the elbow. Use pads on the sacroiliac joints, the outside of the thigh and the outside of the knee to combat sciatic nerve pain while you work out.

Using EMS to Tone Muscle

EMS has been used medically for decades to minimize muscle atrophy after an injury, increase blood flow to promote healing, re-educate muscle, relax spasms and improve flexibility.

However, in 1973, it was revealed that Communist Bloc countries had been using the technique for athletic strength training, with gains of 30 to 40 percent in strength in already trained athletes, as noted in Anderson's research paper.

Don't imagine just sitting on the couch, letting an EMS do all the work for you. For toning and strengthening muscle, studies recommend adding EMS to voluntary exercise for maximum benefits, according to Anderson. That's because while your brain is telling your slow-twitch muscle fibers to go through the moves of your exercise, the EMS machine is firing the fast twitch fibers involuntarily, causing you to work more muscle than you normally would.

Portable EMS units — including some that incorporate TENS technology — are small enough to bring to your workout or use at home. Training centers such as E-Fit and 4U­­Fitness have entire suits filled with electrodes that contract your muscles as you go through a light workout of push-ups, squats and other moves while the unit contracts your muscles. Most fitness centers using EMS recommend a 20-minute workout twice per week.

Here's the Downside

Using EMS to tone muscle might seem like a painless way to gain more muscle, but it's really not. Athletes who have full sensory perception can often be dissuaded from engaging in a regular EMS training program after experiencing pain caused by the treatment. This is due to waveforms also activating neurons that carry pain signals and other sensory info to the brain.

Electrical stimulation waveforms include sine, square and triangle-shaped (spiked), according to Anderson. They can be in the form of a continuous wave or pulsed. A group of pulsed waves — also known as a pulse train — is typically modulated to increase and decrease the current's amplitude.

EMS isn't without risks, however. Rhabdomyolysis is a serious condition resulting from damaged muscle tissue entering the blood stream and causing kidney damage according to a May 2019 review of EMS Studies published in Wiener Medizinische Wochenschrift.

An increase in creatine kinase levels usually brings energy to the muscles, but it can also damage them because of the intense firing during an EMS session. See a doctor immediately if you experience weakness, palpitations or pain after working out with EMS.

Do Commercial EMS Devices Work?

If you've ever watched late night TV, you've no doubt seen ads for ab belts that promise to trim and tone your waistline while you stay glued to the tube. Devices such as the Flex Belt and Slendertone strap across the center of your abdominal muscles, delivering around 150 contractions per 30-minute session (depending on the brand) from perfectly placed electrodes targeting the tummy muscles.

To use EMS on other parts of your body, such as your legs, arms or back, portable units that have lead wires and electrode gel pads let you stimulate any area of the body you want to tone, according to manufacturers. Although ab belts are fairly foolproof, you'll need to consult the manufacturer's electrode placement guide for correct positioning of the electrodes for portable units.

A small February 2018 study of 64 participants published in the Journal of Exercise Rehabilitation showed that an all-over bodysuit of EMS delivering 350 pulses per second may benefit sedentary individuals who are unable to participate in voluntary exercise. However, the level of electrical impulses needed to produce muscle toning is uncomfortable for many users.

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