# Processing of EMG Signals with High Impact of Power Line and Cardiac Interferences
## 2 Material and Methods  
There are two types of muscles in the human body: rapidly contracting muscles responsible for precise movements and contracting ones, whose function is to maintain an upright body position. The EMG signal from fast-twitch muscles is definitely stronger than from those that are constantly tense. Therefore, the EMG measurement method is much more precise in the case of limb muscle injuries. Such diagnostics are most often performed in patients with innervation deficiencies and after injuries or ischemic episodes. Important information for the doctor is the degree of muscle damage and the disorder of its innervation. Since these areas of the body are located distal from the heart, the signal does not interfere with the electrical impulses generated by this organ when measuring muscle tones. During the measurement, it is imperative to use a reference electrode placed in a different body area where muscle contraction activity is low. This significantly increases the accuracy of the test. EMG examination is instrumental in diagnosing the gastrointestinal and urinary system sphincter, as it enables correct diagnosis and implementation of appropriate therapy. EMG tests should be carried out in a patient-friendly environment so the patient can focus on its individual stages. Various sets of EMG signal samples were collected from the abdominal muscles during this research. The placement of the surface electrodes is shown in Figure 5. Such a placement was chosen to visualize the significant effect of electro-cardiac activity on the recorded signals. Also, this part of the body allows the quality of the skin-electrode electrical contact to be changed easily. As a result, the different impacts of power line and environmental disturbances superimposed on electromyography signals could be observed. Figure 4: Example of the zoomed spectrum (**a**) ECG signal with high impact of environmental disturbances. 3 rd order Butterworth HP filter, \(f_{c}\) = 2 Hz, (**b**) superimposed EMG and ECG signals with high impact of environmental disturbances. The measuring system is built of a microcontroller belonging to the dsPIC33 family, equipped with two ADS1292 analog-to-digital converters and the BM78 Bluetooth communication module. The used transducer is a specialized measuring system intended for the measurement of biopotentials--Figure 6. Each of the two ADS1292 chips allows differential measurement in two channels. Thus, the entire device enables the simultaneous measurement of four interesting areas of the patient's body. The transducers are of the delta-sigma (\(\Delta\Sigma\)) type. They provide simultaneous sampling with 24-bit resolution. They also have built-in programmable gain amplifiers. Thanks to these parameters, it is possible to connect the measurement probes almost directly to their terminals through RC input filters, avoiding additional sophisticated amplification circuits. An important parameter of the converters is their sampling frequency, which in this particular circuit is chosen at 2K/s. The measurement resolution of 48 nV/bit was achieved. The actual measurement parameters are greatly influenced by the probes' quality and the accuracy of their adherence to the human body. When the probes show high impedance, the interference caused by the devices located in close proximity, powered from the 50 Hz network, increases greatly. To avoid data acquisition when the probes are disconnected, the device continuously monitors the connection impedance. Thanks to the embedded forced test current mechanism, the system can measure the voltage drop caused by this current. When the measurement circuit impedance is higher than 20 k\(\Omega\), the device stops the acquisition and informs the user about the poor quality of the probe connection. Figure 5: Electrodes placement in the measurement of EMG signal for the right abdominal muscle (lat. _musculus rectus abdominis_). Figure 6: The example of probes placement while measuring.