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?
Dear David,
At this situation, all of your previous trials should be deleted. For all trials, the location of the electrodes should be similar.
Typically, the position of electrodes should be consistent for all the experiments, not just an individual trial.
Dear,
EMG analysis requires a number of methodological rules including skin preparation, careful electrode placement, measurements to show reproducibility and reliability of recordings. Therefore, replacing one electrode with another requires the ability to compare the measurements before and after the electrode replacement. This seems difficult to apply for EMG (there will always be doubt about a comparison) and ideally it is simpler and more rigorous to ignore the first tests. This is part of the protocol incidents, but a "clean" study, (no doubt due to some methodological bias) will avoid misinterpretation.
Dear David,
In this case, it would be better to ignore the data from this collection and start a new exam. Also consider that the individual may already be fatigued due to the activity that was performed at the moment the electrode fell, so it is important to respect a period of muscle recovery that will be evaluated.
Another tip that can help is to mark the position of the electrode with a surgical pen, because then you can place the electrode exactly where it came from.
Thanks everyone for the feedback.
We had a recent test subject who had an EMG sensor fall off during a cutting maneuver. We already completed a majority of the tasks in study as he performed 3 repetitions of 20 different movements (e.g. walking, jumping, stair climb, etc.). We deleted the trial that the EMG sensor fell off, re-placed the same sensor on the location (right erector spinae), and re-ran the trial. Since he had sensitive skin I could see slight red marks from where the Delsys EMG sensor fell off (and this muscle location was shaved). I am confident that the placement was less than 0.1 mm different from the original placement at the right erector spinae. Given that this is not the EXACT sensor placement prior to falling off, we are assuming we should throw away all data afterwards. This is not too much of an inconvenience since we were almost completely done with the study. However, it would be a different situation if this occurred towards the middle of the study or about 10 movement tasks. In that case, is there ever a time where re-placing a fallen marker is acceptable? If I could visibly see the marked area where the sensor was placed (either by sharpie pen or skin color change), would this be okay to affix the fallen sensor back to that marked location?
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