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EMG
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| Electromyograms (EMG) can be recorded from human or animal subjects when using a suitable biological amplifier and a PowerLab data acquisition system.
The electromyogram represents the combined electrical activity produced by multiple action potentials that are generated by contracting muscle fibers. The EMG is not a regular series of waves like the ECG but a chaotic burst of overlapping spike-like signals that are recorded using invasive or non-invasive electrodes.
Bioelectrical signals are typically very small in amplitude (mV) and an amplifier is required to accurately record, display and analyze the EMG. Depending on the hardware and software used, the biological amplifier serves not only to amplify the signal but also to apply a range of filtering options for the removal of unwanted signal artifacts. ADInstruments offer a range of Bio Amplifiers suitable for use with animals and certified safe for use with humans. A PowerLab data acquisition system can be used with other brands and models of amplifier to record the ECG/EKG, provided they have a suitable analog output (Max. ± 10 V). Ask your nearest ADInstruments representative for details.
Recording EMG signals: EMG signals can be recorded using either surface (MLA1010B, MLAWBT9) or needle electrodes (MLA1203, MLA1204). Surface EMG recordings provide information about many fibers in superficial muscles. Surface EMG recordings have amplitudes of a few mV with most of the power between 10 Hz and 300-400 Hz.
Using needle electrodes to record EMG allows the monitoring of potentials generated by fibers that may belong to a few different Motor Units (MUs). It provides local information with good morphological details that allow identification and separation of the contributions due to different MUs, as well as the recognition of MU Action Potential shapes. Recordings using needle electrodes also have amplitudes of a few mV with most of the power comprised between 10 Hz and 1 kHz.
All Bio Amps sold and manufactured by ADInstruments are suitable for use with surface or needle electrodes.
Human EMG
When connecting any type of biological amplifier to a human subject it is extremely important that an independently certified, electrically-isolated amplifier is used. This is necessary to prevent any risk of electrical shock to the subject. ADInstruments Bio Amps have been externally certified and comply with international safety standards, ensuring that our biological amplifiers are safe for connection to humans.
For guidelines and techniques for measuring human facial EMG the following paper is recommended Fridlund A.J. and Cacioppo J. T. Guidelines for human electromyographic research. 1986 Psychophysiology 23(5):567-589.
The following ADInstruments' biological amplifiers are fully isolated for connection to human subjects: - Bio Amp (ML132): A single channel, differential amplifier that is suitable for recording a range of biopotentials such as EEG, ECG, EMG or EOG. For example, a single channel of bicep EMG activity may be measured between two active electrode connections.
- Dual Bio Amp (ML135): A dual channel, differential amplifier that is suitable for recording 2 independent biopotentials that share a common ground. For example, bicep and tricep EMG activity may be simultaneously recorded using two electrodes placed over each muscle group.
- Dual Bio Amp/Stimulator (ML408): A dual channel, differential amplifier that also includes an isolated stimulator suitable for mild electrical stimulation of human subjects (i.e. Evoked EMG studies).
The ADInstruments Bio Amps (Bio Amp, Dual Bio Amp and Dual Bio Amp/Stimulator) are manufactured for use with PowerLab data acquisition systems and are fully software-controlled using LabChart or Scope. These Bio Amps (Bio Amp, Dual Bio Amp and Dual Bio Amp/Stimulator) are recommended for recording up to two biopotentials from a single subject. If recording three or more biopotentials from a single subject, we recommend the ADInstruments Octal or Multichannel Bio Amps (see below). For further information regarding the Bio Amp configuration best suited to your application contact your nearest ADInstruments representative.
Multiple-Channel EMG Recordings
For recording three or more biopotentials from a single subject, ADInstruments provide the following amplifiers that connect directly to PowerLab data acquisition systems. - ADInstruments Octal Bio Amp (ML138): Suitable for measuring up to eight simultaneous biopotential recordings from a single subject (humanor animal). The unit is fully isolated and safe for connection to humansubjects (certification pending).
- 8 Channel Bio Amp (GT205): An 8-channel biological amplifier supplied with two independent ground inputs for recording ECG, EEG, EOG or EMG. Suitable for unipolar and bipolar recordings. (Fully-isolated and independently certified, for connection to human subjects.)
- 16 Channel Bio Amp (GT201): A 16-channel biological amplifier supplied with two independent ground inputs for recording ECG, EEG, EOG or EMG. Suitable for unipolar and bipolar recordings. (Fully-isolated and independently certified, for connection to human subjects.)
The multi-channel bioamplifiers are particularly suited for exercise physiologists that wish to record multiple channels of EMG (Quadricep, Calf, Bicep, Tricepetc) while a subject exercises.
Evoked EMG Recordings
Researchers and teachers are often interested in the effects of nerve and muscle stimulation in relation to normal physiological function. For mild electrical stimulation of human subjects with a fully-isolated unit, the Stimulus Isolator (ML180) or Dual Bio Amp/Stim (ML408) are ideal. These units may be used with the Stimulating Bar Electrode (MLADDF30), the Stimulator Rod with Cable (MLA265) or the Stimulator Cable (4 mm shrouded plug to Alligator Clip) (MLA260).
For nerve and muscle stimulation of animal tissue preparations ONLY, the Animal Nerve Stimulating Electrode (MLA0320) or Stimulator Cable (BNC to Alligator Clip) (MLA250) may be connected directly to the analog output of any PowerLab. LabChart or Scope software may then be used to provide software control of stimulus waveform type, duration and intensity. Please Note: The analog outputs are NOT to be used on human subjects.
Evoked EMG recordings are particularly useful for determining stimulation thresholds, conduction velocities and refractory periods.
Animal EMG
To measure EMG in animal subjects, we recommend the Animal Bio Amp (ML136) supplied with lead wires that terminate in alligator clips. Alternatively, the MLA1605 Shielded Lead Wires can be used with the Bio Amp (ML132), Dual Bio Amp (ML135) and Dual Bio Amp/Stimulator (ML408). The MLA1605 lead wires connect to the Bio Amp subject cable and terminate in alligator clips.
Multiple channel EMG may be recorded using the Octal Bio Amp, 8 Channel or 16 Channel Bio Amps and MLA1505 Lead Wires that terminate in alligator clips or MLA1203 Needle Electrodes.
Software and Data Analysis
LabChart software can rectify and integrate the raw EMG signal and display the results on a separate channel. The RMS power content of the signal can also be calculated and displayed. The LabChart software Spectrum command displays the power spectrum (FFT) of a selected region of data.
Accessories
Physiological monitoring of the EMG requires careful preparation of the subject and appropriate application techniques to ensure high quality signals. A number of accessories are available from ADInstruments, including Abrasive Gel (MLA1093B), Electrode Paste (MLA1095) and Electrode Cream (MLA1090B). For more information about any of the above products, please contact your nearest ADInstruments representative. |
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| PowerLab (MacLab) citations: |
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| Matching different levels of isometric torque in elbow flexor muscles after eccentric exercise. |
| N. Weerakkody, P. Percival, D. L. Morgan, J. E. Gregory and U. Proske, Experimental Brain Research, 149, 141-150, 2003. |
| In humans, the subject’s forearm was secured to a padded board, locked in the 90º position, the maximum voluntary contraction (MVC) was measured. This MVC value was recorded and used to derive the percentage MCV (%MVC) target levels. With the aid of visual feedback, subjects were asked to develop levels of torque representing 2, 5, 10, 20, 30 and 50% of MVC. Once subjects had satisfactorily achieved the target for ~2 s, they were asked to relax……..EMG was recorded throughout the test using 20 mm diameter Ag/AgCl adhesive surface electrodes (3 M Red Dot paediatric electrodes, 3 M HealthCare, Borken, Germany). The skin was shaved, cleaned and abraded before application of the electrodes longitudinally over the belly of the biceps brachii muscle. A pair of electrodes was placed approximately 20 mm apart, and a reference electrode was placed on the dorsal surface of the wrist. The EMG signal was acquired using Chart software (v3.6.3/s), running on an Apple PowerBook using MacLab/8s with MacLab bioamps. The MacLab bioamps were set to apply a 10-Hz high-pass filter and a 500-Hz low-pass filter, with a 50-Hz notch filter. The EMG signal was sampled at 1000 Hz. The signal was full-wave rectified, and the relevant sections averaged. |
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| Focal loss of the glutamate transporter EAAT2 in a transgenic rat model of SOD1 mutant-mediated amyotrophic lateral sclerosis (ALS). |
| D. S. Howland, J. Liu, Y. She, B. Goad, N. J. Maragakas, B. Kim, J. Erickson, J. Kulik, L. DeVito, G. Psaltis, G. J. DeGennaro, D. W. Cleveland and J. Rothstein. Proceedings of the National Academy of Sciences, 99, 1604-1609, 2002. |
| In transgenic rats, electromyography (EMG) and nerve conductions were performed by using an ADI (Greenwich, CT) Powerlab 8/SP stimulator and BioAMP amplifier followed by computer assisted data analysis (CHART 4.0 and SCOPE 3.5.6; ADI). Compound muscle action potentials were recorded by stimulating the sciatic nerve at the sciatic notch and recording from the foot. EMG was performed by using a bipolar needle and sampling at 200 Hz. |
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The material on this page is provided in good faith and believed accurate at the time of writing. No responsibility will be taken, or liability accepted, for damages arising from the use of information herein. Readers are urged to check with respective manufacturers the accuracy of all product related information.
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