Emg - Electromyography

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EMG (Electromyography) Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect medical abnormalities, activation level, recruitment order or to analyze the biomechanics of human or animal movement. The electrical source is the muscle membrane potential of about –90 mV. Measured EMG potentials range between less than 50 μV and up to 20 to 30 mV, depending on the muscle under observation. Typical repetition rate of muscle motor unit firing is about 7–20 Hz, depending on the size of the muscle (eye muscles versus seat (gluteal) muscles), previous axonal damage and other factors. Damage to motor units can be expected at ranges between 450 and 780 mV. Applications: EMG signals are used in many clinical and biomedical applications. EMG is used as a diagnostics tool for identifying neuromuscular diseases, assessing low-back pain, kinesiology, and disorders of motor control. EMG signals are also used as a control signal for prosthetic devices such as prosthetic hands, arms, and lower limbs. Electrical Safety Measurement While isolation physically and electrically separates two parts of a circuit, the two parts can interact. The isolation is achieved by using electromagnetic field coupling between the two circuits. The three most commonly used methods are optocouplers (light), transformers (magnetic flux), and capacitive couplers (electric field). Isolation provides several advantages: • It breaks ground loops. • It improves common-mode voltage rejection. • It permits the two parts of the circuit
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