Lets take a patient in supine position and do needle EMG in Quadriceps muscle.
Standard text book gives At rest there will be no recording after putting the needle.
But we have been taught all muscles are in a state of partial contraction even at rest and no muscle is completely relaxed. If it is true my doubt is that whether the EMG will be able to record that partial contraction.
Does it have anything to do with the ground electrode?
Dear Dr. Kumar,
I share your opinion on the issue of partial contractions at rest. While recording EMG signal from sternocleidomastoid and temporalis muscles during rest, I also had the same experience as you. The interesting point was that, their resting values differed from each other; consequently, I suppose that not only do resting EMG values differ from one individual to another, but also vary in one individual from one muscle to another. It is natural, since all muscles have different tasks and different positions in relation to spine, head, trunk and upper extremities and different contribution to maintain a desired -supine position in your and my case- position.
Regards,
Not sure whether this helps.
Worth keeping in mind that "tone" refers to tension or force in muscle and EMG does not, it is an electrical response; so, EMG may or may not record relaxed muscle force. Of a large number of motor units, if for example only a few motor units are activated and infrequently to keep a small tone, the EMG electrode may or may not pick.
KW
muscle tone is defined as the resistance to passive movement. according to this definition it is implied that it can be recorded only during movement. therefore at rest EMG needle will not recording any electrical activity. it is correct that physiology books talk about partial degree of contraction at rest which cannot be recorded with the EMG needle. however in spastic muscle when the tone is increased EMG needle record electrical activity from the muscle.
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