Transcutaneous Electrical Nerve Stimulation (TENS) is a popular, non-invasive method used for managing pain. It delivers mild electrical currents through electrodes placed on the skin, stimulating underlying nerves. This stimulation disrupts pain signals traveling to the brain or encourages the release of natural pain-relieving substances. Users often apply TENS units for chronic conditions like back pain, arthritis, or fibromyalgia. A common question when starting TENS is whether the current should cause muscles to twitch, making clarification of the expected sensation necessary for effective use.
TENS vs. EMS: Defining Nerve and Muscle Stimulation
The distinction between TENS and Electrical Muscle Stimulation (EMS) is fundamental to understanding the purpose of the electrical current. TENS is specifically designed to target sensory nerves, which are responsible for sending information about touch and pain to the brain. The primary goal of TENS is pain relief, achieved without intentionally causing a muscle contraction.
EMS, by contrast, focuses on stimulating motor nerves and muscle tissue directly. The purpose of EMS is to cause the muscle to contract, which is useful for rehabilitation, preventing muscle atrophy, or strengthening. While both devices use electrical pulses delivered through the skin, TENS aims for a sensory response below the level that activates motor nerves. If a TENS unit causes noticeable muscle contraction, the current is crossing the boundary from sensory stimulation into motor stimulation.
Expected Sensations When Using TENS
When using a TENS unit correctly for pain relief, the goal is to achieve a strong, yet comfortable, sensory sensation. Users should feel a tingling, buzzing, tapping, or prickling sensation under the electrodes. This feeling indicates that the electrical current is successfully stimulating the sensory nerves beneath the skin. The intensity of the current should be slowly increased until the sensation is pronounced but remains non-painful or uncomfortable.
The therapeutic effect is achieved when the intensity is strong enough to mask or compete with the pain signals. High-frequency (conventional) TENS modes aim for this steady, comfortable tingling. Low-frequency TENS, sometimes called acupuncture-like TENS, operates at a lower rate and may produce a muscle twitch if the intensity is high enough. However, this twitching is a secondary effect and should not be forceful or uncomfortable, as the focus remains on sensory nerve stimulation for pain relief.
Troubleshooting Muscle Twitching: Adjusting Settings and Placement
Muscle twitching during TENS use, while occasionally acceptable in some low-frequency modes, often signals that the current is too intense for the pain relief goal. The current has likely reached the motor threshold, the point where the electrical impulse excites motor nerves and causes an involuntary muscle response. If the twitching is uncomfortable or distracting, immediate adjustment of the settings is necessary.
The easiest correction is to immediately lower the intensity dial until the muscle twitching stops and the sensation returns to comfortable tingling. The intensity should be reduced to the highest tolerable level that causes no motor response. If twitching persists even at a low intensity, the electrode placement is likely targeting a motor point or a major peripheral nerve pathway. Electrodes should be placed around the painful area, effectively “sandwiching” the site, rather than directly on it.
Adjusting the electrode position away from bony prominences and areas where nerves are close to the skin, such as the front of the neck or directly over the spine, can help avoid unwanted twitching. If the TENS unit offers control over pulse width or frequency, a wider pulse width or a lower frequency setting can increase the chance of motor nerve stimulation. In these cases, a much lower intensity setting will be required to stay beneath the motor threshold and prevent muscle contraction. By making these simple adjustments to intensity and placement, users can ensure they are achieving the intended sensory stimulation for pain relief.