If you are wondering to make a device that is used to detect and measure electrical activity on muscle. then you will need sensors, So, you can buy them at a reasonable price.
The Advance Technologies EMG Muscle Sensor V3.0 With Cable And Electrodes will measure the filtered and rectified electrical activity of a muscle outputting 0-Vs Volts depending on the amount of activity in the selected muscle, where Vs signifies the voltage of the power source. Power supply voltage: min. +-3.5V.
This Muscle Sensor v3 from Advancer Technologies measures, filters rectifies, and amplifies the electrical activity of a muscle and produces an analog output signal that can easily be read by a microcontroller, enabling novel, muscle-controlled interfaces for your projects
