Electromyography (EMG) Signal Recording
Objective
Study the electrical activity produced by skeletal muscles using surface EMG electrodes. Learn to record, analyze, and interpret EMG signals in both healthy and diseased muscle conditions.
Learning Outcomes
- Understand the physiological basis of EMG signals
- Learn proper electrode placement techniques
- Record and analyze Motor Unit Action Potentials (MUAPs)
- Differentiate normal from pathological EMG patterns
The Science Behind EMG
What is EMG?
Electromyography (EMG) records the electrical activity produced by skeletal muscles. When muscles contract, they generate electrical potentials that can be measured using electrodes placed on the skin (surface EMG) or inserted into the muscle (needle EMG).
Physiological Basis
At rest, muscle cells maintain a resting membrane potential of approximately -70mV. When a motor neuron fires, action potentials cause Na+ to rush in, depolarizing the muscle fiber to +30mV, then K+ flows out to repolarize the membrane.
Motor Unit Concept
A motor unit consists of one motor neuron and all the muscle fibers it innervates (10-1000+ fibers). The signal we record is the Motor Unit Action Potential (MUAP) — the summation of all fiber potentials in one motor unit.
Signal Characteristics
- Amplitude: 0.1 - 5 mV (surface EMG)
- Frequency: 10 - 500 Hz
- MUAP Duration: 5 - 15 ms (normal)
- Firing Rate: 6 - 30 Hz per motor unit
Motor Unit Action Potential (MUAP) — The fundamental unit of EMG
Equipment Familiarization
Click on each piece of equipment to learn about it. Explore ALL items before proceeding.
Click on equipment to learn about it
Patient Preparation & Electrode Placement
Select a muscle to examine, then prepare the skin and place electrodes correctly.
Select a Muscle to Examine
Click on a muscle in the body diagram to select it for EMG recording.
Click on a highlighted muscle to see details
System Calibration
Configure the EMG system parameters for optimal signal recording.
Understanding EMG Settings
EMG signals are very small (microvolts). The amplifier increases the signal magnitude. Surface EMG typically uses 1000-5000x gain.
Removes slow baseline drift and motion artifacts by blocking frequencies below the cutoff. Set to 10-20 Hz for surface EMG.
Removes high-frequency noise and prevents aliasing. Most EMG energy is below 500 Hz. Set to 450-500 Hz for comprehensive signal capture.
Eliminates power line interference that appears as a constant hum in the signal. Always enable unless studying frequencies near 50/60 Hz.
EMG Signal Recording
Record EMG signals during different muscle contractions and conditions.
Signal Analysis
Analyze your recorded EMG data using different signal processing techniques.
Normal
Myopathy
Neuropathy
ALS
Experiment Complete
You have successfully completed all steps of the EMG virtual laboratory experiment.