If this occurs, check that the EMG sensor and reference electrode are adequately attached and connected. Ensure that no clipping is present in the signal. Sampling Rate ensure that the surface EMG signal is sampled at least at 1000 Hz.Īmplifier Gain a gain of 1000 is usually appropriate for surface EMG signals. Reference Electrode ensure the reference electrode, if separate from the EMG sensor, is connected to the instrumentation and to the skin of the subject. As the muscle is contracted, the location of the sensor can be shifted using real-time feedback software to check for signal quality.ĮMG Sensor Technology use advanced high-quality sensor technology with small (1 cm or less), and possibly fixed, inter-electrode spacing. Each Delsys EMG sensor has an arrow on top that should be aligned along the length of the muscle so that the parallel-bar detection sites transect the muscle fibers.Ī significant advantage of the Delsys surface EMG sensors is that they can be used as sensor probes on the muscle of interest prior to final placement. As a result, the electrical activity propagates predominantly along the length of the muscle. Muscle fibers generally run longitudinally in a muscle. When possible, innervation zones should be avoided because in these areas the electrical activity propagates in opposite directions along the muscle fibers and can be attenuated. Also, in this region the muscle is physically smaller, which makes it difficult to accurately place the sensor and avoid crosstalk interference from adjacent muscles. Smaller diameter fibers generate lower amplitude action potentials. In contrast, locating the EMG sensor close to the tendon origins reduces the amplitude of the detected EMG signal because, as the muscle fibers approach the tendon, they become thinner and fewer in number. In the midline of the muscle, fibers have a bigger diameter and generally yield greater amplitude EMG signals. The best location of the sensor on the muscle is generally on the midline of the muscle, far from the tendon origins and the innervation zones, with the sensor arrow parallel to the direction of the muscle fibers. The placement can maximize the physiological EMG signal and minimize cross-talk interference from neighboring muscles. The location of the sensor on the muscle is the single most important factor for good SNR. This unique monitoring tool can be used for assistance in locating the sensor on the muscle, or for real-time feedback of signal quality during recordings. Suggestions for improving signal quality are also provided. A real time summary display of the signal quality is available that includes feedback of the EMG signal SNR, baseline noise, and line interference. At any time during an experiment, visual warnings are provided if signal quality is compromised. The Delsys EMGworks® Acquisition software includes a real-time Signal Quality Monitor tool to provide feedback of the sensor signal quality. For details, see Roy et al.: Electro-mechanical stability of surface EMG sensors in Medical & Biological Engineering & Computing, 45: 447-457, 2007 and De Luca et al.: Sweat test for the electromechanical stability of the EMG electrode-skin interface in Proceeding of the International Society for Electromyography and Kinesiology, 2004. The contoured surface of the Delsys sensors is specifically designed to enhance the contact of the sensor bars with the skin and enhance the adhesion of the sensor to the skin. Without fixed spacing, the inter-electrode distance can change with movement, thereby resulting in unwanted alterations to the EMG signal waveform and its frequency content. The inter-electrode spacing is fixed, ensuring repeatability and consistency in experiments. See De Luca et al.: Inter-electrode spacing of surface EMG sensors: reduction of cross-talk contamination during voluntary contractions in Journal of Biomechanics, 2011. Delsys sensors use a 1 cm inter-electrode spacing, which has been demonstrated through peer-reviewed research to offer the optimal cross-talk suppression while maintaining the EMG signal amplitude. However, the electrode area and inter-electrode distance cannot be too large in order to minimize the detection of unwanted cross-talk interference from adjacent muscles, including muscles deep to the one of interest. The greater the area and the inter-electrode distance the greater the pick-up area of the sensor and, as a consequence, the greater the amplitude of the detected EMG signal. The signal detection selectivity of a sensor depends on the area and the distance between the detection surfaces.
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