System Operation

EMG Measurement

Acquiring EMG


System Operation

No detectable signal is being received (no noise or other signal is present)

  • Check whether the power of the main Receiving Unit is turned "on". The green LED power indicator should be lit.
  • Check the main transmission cable for proper connections.
  • Check whether the Portable unit has the battery pack connected.
  • Check the voltage and the POLARITY of the batteries in the power pack (the most likely cause of this problem).

Massive 60 (50) Hz hum or heavy clipped signal is being recorded

  • Make sure that a grounded pre-amp is used (i.e. pre-amplifier with the green ground lead).
  • Make sure that the ground lead is connected to a reference pellet electrode in a suitable position. Also check that the electrode is adequately attached to the bony reference site. If necessary, apply a new reference electrode or re-attach the reference pellet elsewhere.
  • Place the "ground" pellet electrode on the skin of a bony region of the body, but as close to the recording electrode as possible. Use conductive gel to improve the electrical contact between the skin and the pellet electrode.

One of the EMG signals is not present

  • The quality of contact is likely bad for one or both of the electrode sites. This can be quickly diagnosed using a skin/electrode impedance meter, like the BISIM device offered as an accessory by Bortec. Please contact us for further details.
  • Remove the electrode(s), re-prepare the skin and attach a new electrode. If this does not solve the problem please contact us.

There are artifacts in the signal or the baseline is jumping when I am trying to record the EMG signal

  • There are generally two sources behind recording problems with the EMG signal; the AMT-8 hardware or the acquisition hardware and software. As a general rule, if you are having problems with recording signals with your computer, test the outputs from the AMT-8 directly to an oscilloscope or other display device. If the signals display, then the problem is with the acquisition hardware or software, otherwise there is a problem with the set-up or function of the AMT-8. Ensure that the system is set-up properly and re-evaluate.

What type of Electrodes can be used with the AMT-8?

  • Any type of disposable or re-usable EMG electrode that is combined with an electrolytic gel and has a pellet attachment. However, in accordance with the SENIAM guidelines, Bortec recommends the use of a disposable pregelled Ag/AgCl (silver - silver chloride) electrode, as used in approximately 80% of surface EMG recordings. For more information see Important Factors in Surface EMG Measurement.
  • Bortec offers a bipolar disposable EMG electrode (BIPOLE), meeting all of the specifications of the SENIAM guidelines.

Can I use the AMT-8 to measure Intra-muscular EMG?

  • The Bortec AMT-8 provides complete subject isolation, ensuring subject safety. Bortec offers a pre-amplifier with a robust spring connector attachment allowing the attachment of wire leads (IPE accessories). This can be used with surface EMG electrodes with bare wire ends as well as with wire electrodes.
  • NOTE: Bortec does not assume any responsibility for the use of wire electrodes, and their use is at the discretion of licensed practitioners only.

What is the maximum distance that the subject can be away from the main amplifier and recording equipment?

  • The maximum recording distance with the AMT-8 is 50m. The standard transmission cable length is 10m, but any length can be ordered between 3 and 50m.
  • Please contact Bortec for pricing information.

In what situations are the high gain pre-amplifiers beneficial?

  • The high gain pre-amplifiers (APE-2000) are used when recording from deep lying muscles and/or when the level of muscle contraction (activity) is very low; basically in conditions where the signal is quite faint.
  • One aspect of the EMG signal should be noted. As the distance from the electrode to the muscle area of interest increases, the signal strength decreases, due to a phenomenon called tissue filtering. For more information see Important Factors in Surface EMG Measurement.
  • Please contact Bortec to see if high gain pre-amplifiers would benefit your EMG measurement application.

Can the AMT-8 be used with other physiological measurement equipment?

  • The AMT-8 is commonly used in conjunction with other measurement equipment such as but not restricted to, force plates/mats/arrays, treadmills, electrical and magnetic stimulators, motion capture, video, goniometers, accelerometers, skin impedance, ECG, EEG and respiration equipment.
  • Check the specifications of your data acquisition hardware to see if it has 10 A/D channels for EMG and footswitch inputs from the AMT-8. Configure your software to record and display the EMG and footswitch signals.
  • Please consult the user manuals for your particular data acquisition hardware and software package.

Can I expand the 4 or 8 channel EMG systems?

  • The 4 channel system can be fully expanded to an 8 channel system, as the 4 and 8 channel systems use the same main amplifier and Portable unit enclosures.
  • A 16 channel system can be configured by coupling two 8 channel systems in a sturdy table top case. Wearing two Portable units is the only complication, but customer reports indicate that this is only problematic with recordings in small children. The benefit is that the two 8 channel systems can be used independently. For example, when less than 9 channels of EMG are to be measured in a research study, the second 8 channel AMT-8 system can be used in a teaching lab.

Does the reference pre-amplifier need to be inserted into the 1st channel of the Portable unit?

Yes. The rule is that the reference pre-amplifier must be connected into the Portable unit, provided that there are no other pre-amplifiers connected to a Portable unit channel with a smaller channel number. Most users find it convenient to consistently connect the reference pre-amplifier into channel 1 on the Portable unit.



EMG Measurement


What is the SENIAM initiative and how can I get more information?

SENIAM - Surface EMG for the Non Invasive Assessment of Muscle was a recent concerted action funded by the European Community to better standardize EMG recordings. 9 countries were represented with 60 leading researchers in the field of surface EMG research. For more information see SENIAM site.

Should I use a notch filter to remove 50Hz or 60Hz noise?

No. There is no need for notch filtering with the Bortec AMT-8, or any other system using differential pre-amplification of the EMG signal. Differential pre-amplification allows for the rejection of 50Hz or 60Hz hum (power-line noise) and other external noise sources by rejecting common signal components that are measured from two closely spaced (e.g. 2 cm) electrode sites. One important measure of how well noise components are suppressed is what is termed the common mode rejection ratio.

What are the differences between fixed cable signal transmission and radio telemetry?

Fixed cable systems use a transmission cable between the subject and main amplifier and data acquisition system, whereas, radio telemetry systems transmit the signal from the subject to a receiving unit wirelessly.

The advantage of radio telemetry is that the subject can freely ambulate over a certain area, however, this technology is much more expensive than a fixed cable system. The latest method (i.e. LAN based) of telemetry is more reliable than the old form of radio frequency telemetry, which is susceptible to interference from other equipment and breaks in the transmission (i.e. producing holes in the EMG data).

How do I best record EMG in conjunction with electrical stimulation?

Please consult your stimulator manual for instructions on its operation. For a more detailed description see Important Factors in Surface EMG Measurement.



Acquiring EMG

What types of recording systems can be used with the AMT-8?

The AMT-8 system can be used with any analog or digital display or recording device. Outputs from the AMT-8 are analog with an output maximum peak to peak voltage of 4V.

The output signals are available on the back of the main amplifier and are accessed via standard BNC connectors. You should determine the type of connection on the display or recording equipment and attach a suitable cable to this device. For further information consult the appropriate user manual.

What are the characteristics of the outputs from the AMT-8?

The EMG outputs are in analog form with a maximum peak to peak voltage of 4V, so for digital storage the signals need to be converted from analog to digital form (i.e. A/D converted).

The footswitch outputs are digital and can either be attached to the digital or analog input channel on your A/D card.