The insertion of a needle electrode into a muscle causes accumulation of electrical activity called insertion activity. It is caused by the needle itself whose electrical energy provokes relative changes in the electrical field of the surrounding when placed near the muscle membrane.
Such insertion activity can last up to several hundred milliseconds, but should not last longer (
- A prolonged activity indicates unstable electrical charges at the muscle membrane that could be caused by early nerve or muscle injuries.
- On the other hand a decreased insertion activity might be the consequence of remaining muscle fibres that are insulated by scar tissue or fat after the healing of nerve or muscle injuries.
However, during LEMG examination it can be very hard to detect insertion activity, firstly because it does not last very long and secondly due to the difficult distinction between insertion activity and physiological background activity caused by quiet breathing. Therefore silence is recommended in the examination room. A debriefing of the LEMG data can be helpful too, especially when patterns could not be identified clearly enough during the examination.
The insertion activity can be graded as follows:
- No activity
- Decreased activity
- Normal activity
- Increased activity
- Highly increased activity