EMG Flashcards
Define what is EMG
Electromyography
Neurophysiological technique to record and assess electrical activity produced by skeletal muscles
What does a motor unit comprise of?
Made up of a motor neuron and the skeletal muscle fibers, innervated by that motor neuron’s axonal terminals.
All muscle fibres in a motor unit are of the same fibre type
EMG Signal Composition: What are MUAPT and how is it summed to become a EMG Signal?
When a motor unit discharges, the electrical potentials from all the muscle fibers of the motor unit sum together to produce a compound potential called the motor-unit action potential (MUAP)
The EMG signal is the summation of the discharges of all the motor units within the pick-up range of the electrode.
What are the two types of EMG techniques and what are the pros and cons of each type?
Surface EMG: Non invasive, records from large area
Intramuscular: Records from small area, records from deep muscles
CONS
Surface: Crosstalk b/w muscle groups, unable to record deep muscles, Noise from mechanical artifacts, Contact pressure
Intramuscular: Invasive, uncomfortable over contractions, Position might be displaced over contraction
What are the applications for each type of EMG technique?
Surface: EMGxForce relationship, Kinesiology (sport settings), Neurophysiology of superficial muscles
Intramuscular: Analyzing individual MUAPTs, Clinical settings
Procedures of EMG Data Collection: 1 - Skin Preperation
Shaving excess hair if needed
Cleaning skin with baby wipes
Wiping with alcohol pad to dissolve oil on skin
Apply hypoallergenic tape to remove deda skin
Pad abrasion of the skin: necessary as pads reduce motion artifact
Procedures of EMG Data Collection: 2 - Electrode Placement.
What are the types of electrodes placed?
What are the issues to consider?
Active electrodes and Ground/reference electrode
Active: Avoid innervation zone (parallel and pennate muscles have different IZ) > IZ = unstable and jagged signal with sharp peaks
Ground: Place it on bonny landmark
Refer to an EMG anatomy atlas
Procedures of EMG Data Collection: 2 - Electrode Placement.
What topics would a good EMG anatomy atlas cover?
Type of placement Muscle actions Muscle insertions Innervations Locations Behavioral test Typical signals Potential artifacts Benchmark data
Procedures of EMG Data Collection: 3 - Collecting Data
What are the issues to consider?
Wait at least 5 minutes so that bioimpedance decreases
Consider potential typical artifacts: noise by instruments (electrode displacement), environmental noise (other electrical equipment sinusoidal signal at 50-60hz), cross talk between muscle groups, physiological signals (ECG).
What are the EMG signal processing procedural steps?
- Bandpass low + high 125-250hz
- Full wave rectification (math function - absolute)
- Smoothing & Linear Envelope 8-10samples smoothing, Low pass 12hz
- Normalization (signal amplitude) - Integrate > Average over sample and RMS
Signal Processing/Filtering: Why is band-pass needed?
Minimize noise is the raw signal, done between 0-25hz and 300-500hz
Signal Processing/Filtering: Why is full wave rectification needed?
It converts all signals into positive values / taking absolute value of signal
This enables standard amplitude parameters (mean, peak value, area under curve) to be applied to curve
Signal Processing/Filtering: Why is smoothing and linear envelope through low pass filtering needed?
It smoothes the EMG signal.
Helps to outline mean trend of signal development (as raw EMG burst cannot be reproduced second time, too random)
Signal Processing/Filtering: Normalization, why is it needed? How is it done?
EMG amplitude data greatly influenced by detection conditions, normalization eliminates detection condition influence > rescale to % of selected reference value / standardized for all subjects within study
Reference Values
- Maximal Voluntary isometric contraction
- Given %MVIC
- Mean value of 2-3 EMG signals
- Maximum EMG signals
Recall what are the two types of Parameters in EMG?
Time domain and frequency/spectral domain
In the time domain of EMG parameters, how are the signals processed and what do they represent?
- EMG Integral > rectified signal and calculating area under curve
- Duration & Average EMG > Taking iEMG / time period
- EMG RMS > summing all the squared values of each instantaneous EMG amplitude (in mV or μV) over a set time period, dividing this by the number of seconds in the same time period, and then finally taking the square root of this number (Burden, 2007)
In the frequency/spectral domain of EMG parameters, how are the signals processed and what do they represent?
Fast Fourier Transformation
Analyze & estimate frequency contents of EMG signal
Decompose EMG signal to underlying sinus contents, repeating over certain Hz range > create Total Power Spectrum Graph or Frequency Distribution Graph
What are the evidences for reliability for frequency domain of EMG? What is it related to?
Median of frequency and conduction velocity recorded during muscle contraction > related to muscle fiber type composition and cross sectional area (in animal models)
What are the findings for EMG with regards to Unstable surfaces?
Swiss ball curl ups > lower ROM but higher EMG activation
Unstable shoe surface: Reebok easytone > 28% more activation Gluteus Maximus, 11% hamstring, 11% calf. But study has many flaws, sample size 5 and sample all college students
What are the findings for EMG with regards to Barbell rows?
Increase of external load or cadence affects neuromuscular activitiy
Sets composed pairwise comparisons of randomly assigned
External load: 5, 10 ,20
Cadence: 1, 2, 4 beats
What are the findings for EMG with regards to Fatigue and Soreness?
Strength & force outcome: >72 hours for recovery (CC) and more for EC
Time domain: MU recruitment & sync increases > balance impaired mechanical response
Spectral domain: Action potential decreases speed due to acidosis > shift from high to low frequencies
What are the findings for EMG with regards to Jumps?
Comparing Drop jump and its SSC with changing drop height
SSC Pre-stretch allows muscles time to develop higher activation state
High levels of quad activation > increase anterior translation of tibia during landing > ACL injury risk
Co-activation of bicep femoris muscle > counteract anterior translation > minimize risk
Drop jump intensity determined by contact time during landing, height of jump, athlete BW, muscle pre activation level
What are the findings for EMG with regards to Throwing?
Found two phases,
Agonist burst and Antagonist impulse
Antagonist impulse associate w controlling end of acceleration phase
Increases with throwing velocity
