EMG Sensor falling off... Does it compromise repeatability?

[David Hollinger]

How is data compromised when an EMG sensor falls off during testing? Do you re-place the sensor to the same approximate location and re-run the trial?

The trouble with dynamic biomechanical movement is that fast/abrupt movement can cause a marker or EMG sensor to fall off. It's rare for an EMG sensor to fall off during testing but when it does happen we place it back on the same approximate location where it fell off. We typically delete and re-run the trial when the sensor fell off, but does this compromise all subsequent trials thereafter? What is the general approach in University research labs when this problem occurs? Is it acceptable to re-place the fallen sensor to the location that was originally marked with a pen?

[Allan Carman]

David,

Short answer yes it does compromise the data. You should have a well-defined skin prep and electrode placement routine as both placement and skin impedance will influence EMG magnitude. If an electrode comes off then clean the skin and replace with a new electrode or electrode pair (the sticky and electrode gel would have been lost, I recommend Ambu BlueSensor SP00S ECG disposable electrodes). If the placement and impedance (ideally less than 10K Ohms between the electrode pair and each electrode and earth) are comparable to the original electrode pair then I would normally say carry on.

However, you are doing an EMG reliability study. I would look at what can be done to keep the electrodes on. Try athletic tape over the electrode adhesive pad but avoid the center, as you do not want to squeeze out the gel, athletic tape adhesive spray on the skin around the electrode site or self-adhesive bandage around the whole limb. I would also measure electrode impedance before and after the tails to check that electrodes have not lost skin contact.

Cheers
Allan