EMG - Electromyography

Overview:

Electromyography (EMG) is the study of muscle electrical activity. Its origins can be traced back to the late 18th century work of Galvani, who demonstrated a relationship between muscle contraction and electricity. However, it wasn’t until the 1920s, when Gasser and Newcomer displayed muscle electrical activity on a cathode ray oscilloscope, that the noninvasive field of surface EMG (SEMG) was born.

In an SEMG recording, a bipolar electrode is placed on the skin surface overlaying a muscle of interest. As the muscle contracts, myoelectric activity is revealed as complex waveform with an amplitude range of >0-10 mV.

Alternatively, intramuscular EMG techniques may be used where increased signal specificity is required. This requires the use of fine needle electrodes placed within the muscle of interest. 

There are two basic applications of EMG recording: Neurological EMG, involving the measurement of muscle response timing following artificial stimulation of a motor point; and kinesiological EMG, involving the measurement of muscle activity with functional limb movements, postural tasks, and exercise training. Examples of specific applications of EMG in basic and clinical research include:

  • Biofeedback muscle stimulation
  • Pain and proprioception
  • Sports science and training
  • Ergonomics
  • Age and mobility
  • Biomechanics of joint movements
  • Neurological disorders, posture, gait and limb movements

Method:

EMG is suited to the study of generally any skeletal muscle that can be accessed with surface or intramuscular electrodes. ADInstruments offers complete data acquisition solutions for SEMG and intramuscular EMG, for use in human and animal research.

SEMG

Surface EMG recordings provide information about aggregate motor unit activity in superficial muscle. The advantage of SEMG is its convenience and good overall correlation to generated muscle force. Signal amplitudes recorded with SEMG typically range from >0 to 10 mV, with most signal power between 10 to 400 Hz.

Electrode Placement
Bipolar surface electrodes (Ag-AgCl) should be positioned between a motor point (Fig. 1; source of alpha motor neuron innervation of the muscle) and tendon insertion, or between two motor points. Both electrodes should also be placed along the midline of the muscle in order to prevent signal crosstalk between adjacent muscles (e.g., Fig .2). By placing both electrodes parallel to the longitudinal axis of the muscle this also ensures the detection surfaces will intersect common muscle fibres.

Note: Placing electrodes directly over a motor point may result in increased frequency components in the signal. Action potentials spread in opposite directions from the motor point. A bipolar electrode placed over a motor unit, depending on the geometric relationship, may result in an increased number of recorded potentials due to phase addition and subtraction of the action potentials. Motor units can be identified using artificial stimulation: the point on the muscle whereby the application of minimal electrical current produces a perceptible muscle twitch will correspond to a motor unit.

Figure 1. Schematic representation of a motor unit, consisting of a single spinal alpha motor neuron and the muscle fibers it innervates. The source of innervation in the muscle is the motor point. 

 Figure 2. Illustration of SEMG involving bipolar surface electrodes located on biceps brachii and triceps brachii

Intramuscular EMG

Unlike SEMG, intramuscular EMG recordings provide high spatial selectivity allowing for individual superficial or deep muscle groups to be recorded from. Because the current source is highly localized with respect to the electrode tip, i.e., only involving a few muscle fasicles, the recorded EMG waveform will appear less complex and is therefore more amenable to studies relating motor unit firing rates to generated muscle force. A second advantage of intramuscular EMG is that multiple recording sites within the same muscle group may used.

Like SEMG, recordings using needle electrodes also have amplitudes within the >0 to 10 mV range, although due to being closer to the current source amplitudes will predictably be more toward the high end of this range. As with SEMG, most of the signal power will also be between 10 Hz and 400 Hz. 

Electrode Placement
Needle electrodes (29G) or fine wire electrodes (platinum or stainless steel, <100 μm diameter) or ) inserted through the skin via carrier syringe (26G) may be used (e.g, Fig. 3). Insertion though a hair follicle may result in less irritation. Insertion site should be sterile to prevent infection. The same basic rules for bipolar placement geometry that apply to SEMG also apply to intramuscular EMG. Usually after the electrical activity caused by the irritation of needle insertion subsides, no abnormal spontaneous activity should be detected. Action potentials begin to appear when the muscle contracts and increase in frequency with greater force of contraction.

 Figure 3. Illustration of intramuscular EMG involving bipolar needle electrodes inserted into biceps brachii and triceps brachii.  

Evoked EMG

Researchers and teachers are often interested in the effects of nerve and muscle stimulation in relation to normal physiological function. Evoked EMG recordings are particularly useful for determining stimulation thresholds, conduction velocities and refractory periods.

For mild electrical stimulation of human subjects with a fully-isolated unit, the ADInstruments Stimulus Isolator or Dual Bio Amp/Stim are ideal. These units may be used with the Stimulating  Bar Electrode, the Stimulator Rod with Cable or the Stimulator Cable (4 mm shrouded plug to Alligator Clip).

For nerve and muscle stimulation of animal tissue preparations ONLY, the Animal Nerve Stimulating Electrode or  Stimulator Cable (BNC to Alligator Clip) may be connected directly to the analog output of any PowerLab. The analog outputs are NOT to be used on human subjects. Stimulus waveform type, duration and intensity are software controlled.

EMG signal analysis

In the case of SEMG, it is common practice to quantify the rectified integrated signal. Signal rectification can be easily performed during acquisition with a PowerLab, using a RMS transformation. Computing the integral is likewise simple to perform in LabChart using an arithmetic channel calculation. This allows the muscle force (represented by the height of the integrated signal) and duration of contraction to be easily estimated. Measuring the firing frequency in order to correlate to muscle force is not recommended in SEMG due to the aggregated nature of the recorded signal. For this type of analysis, intramuscular EMG is recommended.  

 

Note: ADInstruments Bio Amps (ML132, ML135, ML136, ML138 and ML408) are not suitable for any biopotential recordings that require a driven guard circuit.

Software:

The LabChart Advantage:

(may require additional Modules and Extensions)

  • Raw EMG signals can be rectified using an RMS transformation during acquisition
  • LabChart's channel Arithmetic function allows for area under curve (AUC) to be easily calculated using integration
  • Quantitative EMG analysis with the Data Pad
  • AUC amplitude can be related to force (with suitable conversion factor)
  • AUC width relates to contraction duration
  • Macros can automate many tedious and repetitive analysis tasks
  • Automated extraction of data from recordings using online Timed Add to Data Pad or offline using Multiple Add to Data Pad
  • LabChart data files can be marked with events using the Comments feature

LabChart

LabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of LabChart Pro and LabChart Extensions are free for download from the website for existing LabChart users.

Scope View

Scope View (LabChart Windows) provides the features of a digital oscilloscope to facilitate recording and viewing consecutive sweeps of data. These sweeps, or pages, can be overlaid and averaged within LabChart. Scope View is used commonly to measure any high-frequency signal that is time-locked to a stimulus, such as muscle action potentials and evoked EMG responses. For analyzing Evoked EMG Potentials, the Scope View feature is recommended because it provides signal averaging functions that are necessary to extract the evoked response from background noise.

There are several powerful features in Scope View that enhance analysis and display including:

  • Provides the ability to record, display and analyze any high frequency signal that is time-locked to a stimulus
  • Synchronizes sweeps with recorded or built-in stimulation patterns.
  • 3D Depth and Saturation Overlay feature in the Scope Overlay Options to help distinguish overlaid traces.
  • Alter the active trace and overlay trace colors.
  • Change the display background to black for better contrast.

 

GLP and 21 CFR Part 11

For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Hardware:

PowerLab Data Acquisition Systems

The PowerLab is a high-performance data acquisition unit capable of recording at speeds of up to 400,000 samples per second continuously to disk (aggregate). PowerLab units are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other third-party companies. In addition to standard single-ended BNC inputs, 4 differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. Research PowerLab units include:

Signal Conditioners

Bio Amplifiers

Human EMG

The following ADInstruments' biological amplifiers are externally certified to comply with international safety standards and are fully isolated for connection to human subjects:

FE132 Bio Amp

FE135 Dual Bio Amp


ML408 Dual Bio Amp/Stimulator

Multi-Channel EMG

ML138 Octal Bio Amp

  • A differential amplifier that consists of eight electrically isolated differential input AC amplifiers
  • A shared ground connection across all eight inputs.
  • Supplied with two packets of MLA0310 Lead Wires (1.8 m, 10 snap on)


Note: The Bio Amp, Dual Bio Amp and Dual Bio Amp/Stimulator are manufactured for use with PowerLab data acquisition systems and are fully software-controlled by LabChart. These Bio Amps cannot be used for recording 3 or more biopotentials on a single subject; however, they may be used for multiple subjects that have separate grounding leads.

Note: The ADInstruments Bio Amps (ML132, ML135, ML136, ML138 and ML408) are not suitable for any biopotential recordings that require a driven guard circuit.

Animal EMG

FE136 Animal Bio Amp

Instruments

Multiple-Channel EMG

ADInstruments also provides multiple channel bioamplifiers that connect directly to PowerLab data acquisition systems. These units are also 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, Tricep etc.) while a subject exercises.

GT201/F 16 Channel Bio Amp

Accessories

Bio Amp Cables:


Leads:

Leads compatible with both shielded (MLA2340 & MLA2540) and unshielded (MLA1340 & MLA1540) cables:


Leads compatible with shielded cables (MLA2340 & MLA2540) only:


Leads that directly connect to the Dual Bio Amp


Leads that directly connect to the Animal Bio Amp


Electrodes:


Consumables:

Diaphragm electromyogram in infants with abdominal wall defects and congenital diaphragmatic hernia
Z. Kassim, C. Jolley, J. Moxham, A. Greenough, and G.F. Rafferty, European Respiratory Journal, 143-149, 2011

The Effect of Associative and Dissociative Attentional Focus Strategies on Muscle Activity and Heart Rate During a Weight Training Exercise
Neumann D. L. and Heng S., Journal of Psychophysiology, 1-8, 2011

Neuromuscular consequences of an extreme mountain ultra-marathon
Millet GY, Tomazin K, Verges S, Vincent C, Bonnefoy R, Boisson RC, Gergele L, Feasson L, Martin V., PLoS ONE, e17059, 2011

Citations Database


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.

Research Solutions
Education Solutions
Pharma Solutions
Citations Database
Top Solutions:
Site Feedback
X

Site Feedback

http://www.adinstruments.com/solutions/pharma/Cardiovascular-and-Renal-Physiology/EMG/

* Denotes a required field
* Name
* E-Mail
* Operating System
* Web Browser

* Comments