The commonly used sensor placement positions are annotated in the image. The most frequently found are the AB (index - middle finger), AC (index - 3rd finger), and DE (thenar eminence). EMG
The EMG electrodes should be placed alongside the muscular fibers with a 2 cm spacing between them (G and H). They should be preferentially placed on the belly of the muscle. This corresponds to the more central area of the muscular fibres and may be found by performing a muscular contraction. The third electrode (F) is the referential and should be placed in an area of low muscular activity, usually a bony area. Please bear in mind that this image is only an example and so as long as these rules are followed the sensor may be placed in any muscle.
Furthermore, if the application consists only in detecting a muscular activation the placement of the three electrodes in line should be sufficient. You may see some examples of this last option in here:https://www.how.do/guide/bitalino-train-that-tempohttps://www.youtube.com/watch?v=ectJrNScZpwhttps://www.youtube.com/watch?v=GHrtN-rZHiEhttps://www.youtube.com/watch?v=co_f_aaHEEAECG
For ECG we suggest a triangular electrode placement such as the image bellow illustrates where the ground should be the electrode in the middle (I). The order of the other two electrodes is irrelevant (J and K).
Regarding the use of the electrodes, they are disposable and may be used only once. The skin should be cleaned with alcohol before the placement and also should be safeguarded that the skin is dry. It is also good to ensure that there is an area without any hairiness.