A Transcutaneous Electrical Nerve Stimulation (TENS) unit is a portable, battery-powered device that uses low-voltage electrical currents to help manage pain. The unit delivers these currents through electrode pads placed on the skin, stimulating the nerves to either block pain signals or encourage the body’s release of natural pain-reducing chemicals called endorphins. This non-invasive, drug-free method offers temporary relief for muscle strains and soreness like those experienced in the hamstring. Since the electrical currents travel between the pads, the effectiveness of TENS therapy depends highly on precise pad placement.
Understanding the Hamstring Muscle Group
The hamstring is not a single muscle but a group of three distinct muscles that run down the back of the thigh from the pelvis to just below the knee joint. These muscles collectively function to extend the hip and flex the knee, making them crucial for running and walking. The three components are the semitendinosus, the semimembranosus, and the biceps femoris.
The semitendinosus and semimembranosus muscles are positioned on the inner (medial) side of the back of the thigh, while the biceps femoris is located on the outer (lateral) side. All three muscles typically originate from the ischial tuberosity, or “sit bone,” in the pelvis. Knowing the location of these muscles is important because pad placement must target the specific muscle causing pain. For instance, pain high up near the gluteal fold indicates a possible injury near the origin point, while pain near the back of the knee suggests a problem near the insertion point.
Pad Placement for Localized Pain Relief
When hamstring pain is acute and concentrated in a small area, such as a trigger point or tendon junction, a focused placement technique is most effective. This method aims to surround the immediate area of discomfort to overwhelm local pain signals. The most common approach is the bracketing technique, where two pads are placed on either side of the painful area, but never directly over the point of maximum pain itself.
If the pain is in the middle of the muscle belly, place one pad a few inches above the painful spot and the second pad an equal distance below it, keeping them in a vertical line parallel to the muscle fibers. The pads must be at least one inch apart to ensure the electrical current travels through the tissue. If the pain is radiating down the back of the thigh, which may be referred pain from the sciatic nerve, pads can be positioned along the nerve’s path in the upper thigh or gluteal area. Placing one pad high on the gluteal area and the other lower on the hamstring can help intercept the pain signal.
Pad Placement for Muscle Spasm and Recovery
When the goal shifts from treating a sharp, localized injury to addressing broader muscle soreness, stiffness, or spasms following strenuous activity, a different strategy is needed. This technique focuses on covering a larger segment of the muscle to promote a generalized reduction in tension and discomfort. The most practical application for widespread soreness is a linear or parallel arrangement that spans the length of the affected hamstring muscle.
To treat a large area, one pad should be placed near the muscle’s origin, high under the buttocks, and the second pad near the muscle’s insertion, just above the back of the knee. The pads should be aligned vertically to follow the natural direction of the muscle fibers, allowing the current to pass through the entire muscle belly. This wider spacing aims for gentle, rhythmic stimulation that encourages muscle relaxation. TENS is for pain relief and sensory nerve stimulation, distinct from Electrical Muscle Stimulation (EMS), which elicits strong muscle contractions.
TENS Unit Settings and Safety Guidelines
Once the pads are correctly positioned, adjusting the TENS unit’s settings is the next step for effective pain relief. For acute, sudden hamstring pain, conventional TENS therapy settings are used: a high frequency (80 to 120 Hz) combined with a low pulse width (50-100 microseconds). This combination aims to engage the pain gate mechanism, creating a buzzing or tingling sensation that overrides the pain signal.
For more chronic hamstring discomfort or deep muscle soreness, a lower frequency (2 to 10 Hz) and a higher pulse width (200-500 microseconds) may be used to stimulate the release of endorphins. The intensity should always be increased gradually until the sensation is strong but comfortable, never causing pain or a forceful muscle contraction.
Treatment sessions usually last between 20 to 60 minutes and can be repeated several times a day as needed. For safety, TENS pads must never be placed on the front of the knee, over broken or irritated skin, or near critical organs like the eyes or the front of the neck. Individuals with pacemakers or other implanted electronic devices should consult a healthcare provider before using a TENS unit.