EMG data FAQ

This FAQ attempts to provide answers to questions about EMG data quality - it does not provide information about the interpretation of EMG data as there are plenty of very good books on this subject.

How do I set up the Windaq/Pro software to record EMG data?

You need to make sure that the Windaq/Pro software is sampling the data fast enough - this is controlled by two settings:

  1. Edit:Preferances:Maximum Sample Rate needs to be set to the highest rate that you are likely to need - somewhere in the 50000 to 80000 range works well in most cases. For example, if you are recording 10 channels of EMG + 2 event switch channels then this works out at a per channel sample rate of 50000/12 (just a bit over 4,000 samples per channel).
  2. Edit:Sample Rate can now be set to the actual rate that you want to capture data at - this can be anything up to the Maximum Sample Rate that you set above. This rate (like the maximum rate) is the overall throughput rate for the ADC so you count up the number of channels that you are collecting from (we'll assume four channels for this example) and multiply it by the signal bandwidth that you use (controlled by the Bandwidth switch on the BPU - let's assume you have set this to #6 or 500Hz) - then double the result thus ... 4 * 500 * 2 = 4,000 - any sample rate that is greater than 4000 will produce a good EMG recording.

Once you have set the sample rates and channel selections you can make the software default to using these settings each time that you start up via the File:Save Default Setup option.

What is the range of the EMG signal levels on the human body reading in term of (uV) microvolts?

The signal level that can be detected on the surface of the body depends on many different factors. In our experience the detected signals can range from a few uV to several mV, depending on the strength of the contraction and the position of the sensors relative to the muscle, etc.

How can I make a fine wire recording with surface electrodes?

If you are using an MA-300 system then simply order the fine-wire pre-amplifiers and connect the wires to the thumb-screws provided.

I have an older MA-100 EMG system - can I use it for fine wire studies?

We recommend that you upgrade to a new MA-300 system and offer substantial discounts on new systems to existing users. However, it is possible to use fine wire electrodes with the MA-100. These instructions assume that you are using standard MA-110 electrodes:

Place the MA-100 preamplifier close to the insertion site with the three stainless steel electrodes up (i.e. the back of the electrode on the subjects skin surface). Assuming that you are using a common bi-polar fine wire electrode then you would connect the two fine wires to the outer two stainless pads (these are the preamplifier inputs). If you remove the insulation from the fine wire then you can often simply tape the un-insulated wire ends directly to the pre-amplifier. The center stainless steel electrode disk must then be connected to the subjects skin surface to provide a ground reference point - alternatively you can use a separate ground electrode attached to the MA-100 back-pack case (the MA-100 does not provide a separate ground reference - however all MA-300 systems include a ground reference connector as standard using a normal DIN electrode connector).

Many people have reported good results by simply taping the fine wire to the outer two pads while leaving the center pad uncovered. If the outer two pads are completely insulated by the tape then it's possible to turn the preamplifier over and attach it to the subjects skin in such a way that the center ground reference electrode is in contact with the subject. It is also possible to unscrew the three stainless steel disks on the preamplifier and replace them with thumbscrews or springs although this is not recommended as it is easy to damage the pre-amplifiers.