Muscle Physiology

Muscle Physiology: Overview

Electromyography (EMG) is an electrodiagnostic technique for evaluating and recording the electrical activity produced by skeletal muscles. An electromyograph detects the electrical potential generated by muscle cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect medical abnormalities, activation level, or recruitment order or to analyze the biomechanics of human or animal movement.

Electromyography. (2015, May 1). In Wikipedia, The Free Encyclopedia. Retrieved 17:17, June 22, 2015, from

Maximal voluntary contraction
One basic function of EMG is to see how well a muscle can be activated. The most common way that can be determined is by performing a maximal voluntary contraction (MVC) of the muscle that is being tested.  It is easy to perform MVC calculations in LabScribe.

Muscle force

EMG recording with IX-BIO8

Muscle force, which is measured mechanically, typically correlates highly with measures of EMG activation of muscle. Most commonly this is assessed with surface electrodes, but it should be recognized that these typically only record from muscle fibers in close approximation to the surface. EMG analysis using LabScribe

EMG can also be used for indicating the amount of fatigue in a muscle. The following changes in the EMG signal can signify muscle fatigue: an increase in the mean absolute value of the signal, increase in the amplitude and duration of the muscle action potential and an overall shift to lower frequencies. Monitoring the changes of different frequency changes the most common way of using EMG to determine levels of fatigue. The lower conduction velocities enable the slower motor neurons to remain active.
A motor unit is defined as one motor neuron and all of the muscle fibers it innervates. When a motor unit fires, the impulse (called an action potential) is carried down the motor neuron to the muscle. The area where the nerve contacts the muscle is called the neuromuscular junction, or the motor end plate. After the action potential is transmitted across the neuromuscular junction, an action potential is elicited in all of the innervated muscle fibers of that particular motor unit. The sum of all this electrical activity is known as a motor unit action potential (MUAP). This electrophysiologic activity from multiple motor units is the signal typically evaluated during an EMG. The composition of the motor unit, the number of muscle fibres per motor unit, the metabolic type of muscle fibres and many other factors affect the shape of the motor unit potentials in the myogram. EMG analysis using LabScribe


Electroculogram Activity (EOG), is measured by electrodes placed on the skin near the eye.  These electrical changes are unique to each of four different types of eye movement (saccades, VOR, pursuit, and vergence).  The IX-BIO4/IX-BIO8/iWire-BIO4/iWire-BIO8, are DC coupled, allowing the measurement of EOG’s.

Strength and Performance Testing

Strength and performance testing and evaluation in athletes of all types can be performed with the iWorx EMG system. The IX-BIO4 and the IX-BIO8 offer a portable, color coded system, with the ability to generate reports and export data.

Muscle Physiology: Systems

IX-BIO4 IX-BIO4  4 Channel Biopotential Amplifier
IX-BIO8 8 Channel Biopotential Amplifier
IX-TA-220 10+ Channel Recorder

  • Record EMG with iWire-BIO4 or iWire-BIO8
  • Stimulate with Built-In Isolated Stimulator
  • Expandable for multiple measurements
IX-RA-834 8 Channel Recorder IX-RA-834 8-Channel Recorder with iWire-BIO4 or iWire-BIO8

Muscle Physiology: Software

LabScribe software is a powerful recording and analysis software package offered by iWorx. LabScribe has an intuitive, user-friendly interface for setting up acquisition screens, calibrating signals and analyzing data. Up to 128 channels of data can be displayed simultaneously at sampling rates as high as 100,000 samples/second.

A comprehensive set of analysis routines have been preconfigured making data analysis and interpretation quick and easy. LabScribe includes a scripting function for use if the built-in analysis tools fall short of what is required for your application. Scripting languages currently supported include: Dadisp, Python, MatLab, LabView, and C++

In addition, data from iWorx Recorders can be acquired with LabView or Matlab or C++ programs using the provided iWorx API.


EMG analysis using LabScribe

Perform maximal voluntary contraction (MVC) calculations in LabScribe.


Muscle Physiology: Citations

Papers about measuring EMG using iWorx systems on Google Scholar
Papers about measuring EOG using iWorx systems on Google Scholar

Featured Citations:

Counts, BR, Buckner, SL, Dankel, SJ, Jessee, MB, & … (2016). The acute and chronic effects of “NO LOAD” resistance training. Physiology & …. Elsevier.

DP Looney, WJ Kraemer, MF Joseph and …, “Electromyographical and perceptual responses to different resistance intensities in a squat protocol: Does performing sets to failure with light loads produce the same …”, The Journal of … (, 2016).

CD Black, BK Tynes, AR Gonglach and DE Waddell, “Local and Generalized Endogenous Pain Modulation in Healthy Men: Effects of Exercise and Exercise-Induced Muscle Damage”, Pain Medicine (, 2016).

NC Dabbs, CD Black and JC Garner, “Effects of whole body vibration on muscle contractile properties in exercise induced muscle damaged females”, Journal of Electromyography and … (Elsevier, 2016).