Measurement of Muscle Activity Flashcards
What are some of the non-sporting uses of EMG?
Ergonomics
Clinical settings
Surgery prep
Products
What do we use EMG for in sport?
Is a muscle active and when is it active?
Does it fatigue?
Is there coactivation present?
What conclusions cannot be drawn from sEMG?
Increased responses doesn’t imply an increase in motor unit recruitment
What conclusions can be drawn from sEMG?
If a muscle is on/off
Timings of activation
Muscle excitement
What are some of the neural factors affecting force generation?
Number of neurons
Size of the neurons
Rates of action potential discharge
How is a signal generated?
Nerve impulses cause muscle fibre contraction
Motor end point stimulation reduces the electrical potential of the cell (depolarisation)
What is termed the waveform, Spatio temporal summation and repetitive sequence?
Muscle Action Potential (MAP)
Motor Unit Action Potential (MUAP)
Motor Unit Action Potential Train (MUATP)
What is the electromechanical delay?
Delay in the sending of the impulse and then seeing the movement occur
What is the process of EMD?
Detection of fluctuations (electrodes)
Signal Transmission
Signal Modification
Storage of Waveform
What are the intrinsic factors affecting the EMG signal?
1) Physical –> no. of active MU’s, fibre type, blood flow
2) Anatomical –> fibre diameter, depth of fibres
What are the extrinsic factors affecting the EMG signal?
1) Indwelling –> deep muscles and isolated MU’s
2) Surface –> focus on large muscle groups (lowers sin prep but increases crosstalk risk)
3) Passive –> prone to placement errors and crosstalk
What are the 3 causative extrinsic factors of EMG signal/measurements?
1) Electrode Location –> must be on muscle belly
2) Impedance –> correct skin preparation is vital
3) Orientation –> parallel with the muscle fibres
What must we do to standardise EMG recordings?
Isometric tests (single joint exercises) Sample at 1000Hz (due to Nyquist theory)
What is crosstalk?
How can it be reduced?
Detected signal contains noise from another muscle
Reduce electrode size and place on muscle belly
What is noise?
What are the frequencies at ambient, motion and physiological times?
Any signals not part of the physiological signal
50/60Hz, 0-20Hz, 80Hz
How can you reduce noise of an EMG signal?
1) Tape the electrodes down
2) Differential Amplification –> subtract 2 sites and then amplify that answer to amplify it
3) FIlters –> Tissues (low pass), Electrode (high pass)
How do you process the signal related to the time component?
Where you estimate the amplitude of the signal
1) Raw EMG –> basic identification
2) Rectification –> AREMG (average rectified value), RMS (root mean square), Linear Envelope
How do you process the signal related to the frequency component?
Indicator of fatigue
Median, Mean, Zero Crossings, Time to Peak
What is the role of the frequency spectrum?
Low frequencies contribute a low amplitude to the trace
Likewise with high frequencies
However when all things happen at once it fills the spectrum completely with ranges of amplitudes
How does fatigue affect the frequency spectrum?
Compression of the spectrum towards the lower frequencies due to:
- fatigue of high threshold MU’s
- reduced conduction velocity
What are the advantages and disadvantages of EMG normalisation testing?
ADV –> compare muscles/subjects
DISADV –> eliciting a MVC differs, poor repeatability of EMG within MVC’s
What does threshold analysis accurately assess?
When the muscle is active/inactive
Define a threshold and assess when a signal is above that
What is the EMG-tension relationship?
Muscle tension and EMG signal are both affected by the same factors:
No. and firing rate of muscle fibres/MU’s
