The most direct and effective way of achieving high quality EMG signals is to select advanced technology and use it properly.
Delsys provides the most advanced and helpful sensor technology that eliminates much of the unwanted signal noise sources. We also offer the Signal Quality Monitor tool in the Delsys EMGworks® Acquisition software to monitor the quality of the recorded EMG signal in real-time and provide suggestions for improvement.
The Delsys sensor technology incorporates over 20 years of development for high-quality recording of surface EMG signals. Specific designed features of our sensors are identified below which can significantly enhance the reliability, robustness and quality of the EMG signal detection.
The Trigno wireless sensors contain two stabilizing references in addition to the differential EMG pair. This proprietary design allows the sensor to react instantaneously to disturbances detected on the surface of the skin, reducing the impact of these noise sources on the detected EMG signal quality.
In addition, we have incorporated a 20 Hz high-pass filter that attenuates motion artifact without distorting the physiological EMG signal.
This is documented in one of our recent research publications. See De Luca et al.: Filtering the surface EMG signal: movement artifact and baseline noise contamination in Journal of Biomechanics, 43(8): 1573-1579, 2010.
The signal detection selectivity of a sensor depends on the area and the distance between the detection surfaces. 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. 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. 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.
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.
The inter-electrode spacing is fixed, ensuring repeatability and consistency in experiments. 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 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.
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 Delsys EMGworks® Acquisition software includes a real-time Signal Quality Monitor tool to provide feedback of the sensor signal quality. At any time during an experiment, visual warnings are provided if signal quality is compromised. A real time summary display of the signal quality is available that includes feedback of the EMG signal SNR, baseline noise, and line interference. Suggestions for improving signal quality are also provided.
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.