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What does EMG stand for?
What is EMG?
- a recording of the voltage changes associated with the activation of skeletal mm fibres
What are the clinical uses for EMG?
- - electrodiagnosis
- - analysing and quantifying mm function
- - research
- - clinical assessment
- - biofeedback pt understand what it is to contract a mm, feeling and how to do it again
- - all of these applications involved the detection of an electrical signal which is processed then averaged and smoothed
- - voluntary activation of skeletal mm result for the activation of alpha motor neurons. Innervating skeletal mm fibres. The motor neuron axons then excite skeletal mm fibres at the neuromusclar junctions. Each of the muscle fibres excited undergoes a marked increase in the permeability of their membranes to sodium and potassium ions. Due to the electrochemical forces acting on these two ions, they move into and out of muscle fibres effectively changing the concentrations of ions in the extracellular fluid. These changes in ion concentration can be detected by surface electrodes connected to a voltage measurement device. It is the voltage changes monitored in this way that constitutes the EMG.
What is MUAP?
- - motor unit action potential
- - contraction of a motor unit in response to an AP
The electrical signal of EMG
- - are 1mV or less- small
- - easily swamped by electrical noise
What is electrical noise and what are some sorces?
- - noise= unwanted electrical signals
- - common forms of noise from radio and TV, transmitters, power lines, light globes, fluoresent lights
How do you minimse electrical noise?
- - two active over the mm
- - one reference located elsewhere on the body- boney bits
- - signal + noise - one input
- - another signal and noise- 2nd input
- - the differential amplifier substracts the two inputs and amplifies the difference so the noise is eliminated and the signal (s1- s2) reflects the EMG
- After correcting for the input of the reference electrode in the total signal
What is Filtering?
- - EMG signals are in the range 0-500Hz/ secf
- - Frequencies greater than 500Hz are filtered out- not biological
- - frequencies lower than 20Hz are usually filtered- movement etc
- Most EMG signals are in range 50-150Hz
What are sampling rates?
- - may be fixed or set depending on equipment
- - an average over a longer period produces a more even output is usually easier for a pt to work with
How do you interprete the signals of EMG?
- - raw signal- each spike isa MUAP- is a pattern of overlappingspikes
- - appears chaotic due to motor units firing asychronously and at different frequencies
The integrated EMG is obtained by rectifying the raw EMG signal (i.e. converting all the negative spikes to positive then averaging the spike activity)Top one is integrated signals- smoothed out after it has ben rectified- flipped-ve on bottom picture- voltage changes- ion concentrations. The above tells you the time of the contraction and the strength/ force of the contraction. Area under line- overall energy used for the contraction Integrated EMG has three important features;It shows the time course of the muscle activationIt gives an indication of the peak force productionThe area under the graph gives an indication of overall energy expenditure in a contractionThe integrated signal may be used to drive a bar graph
What are the 3 types of EMG electrodes?
- - surface- no so valid- can repeat easily
- - needle- needles in skin
- - intramm fine wire- can identify a particular mm- very valid
- - the further apart the active electrode, the more MUAPs will be picked up and amplified
- - the further apart the more MUAPs will be picked up and amplified so stronger signal is obtained- greater chance of picking up other noise. Crosstalk-picking up signals from other mm
- - closer together- small signal but more accurate
What are the 3 arangements for SEMG
- - separate active electrode and a separate reference- freedom to put whereever- best
- - a bi- electrode with 2 active electrodes together- can change distance
- - tri-electrode- all 3 are stuck together- shit
- - gel
- - active electrodes should be aligned along/ down the mm belly to detect the change of voltage via depolarisation. If across- crap signal
- - reference- boneys close by
How do you prepare the skin for EMG?
- - skin should be wiped with an alcohol swab- clean dead skins cells and oil off the skin
- - abrasion and hair shaves not usually used
What is normalisation?
- - involves referencing the EMG data to a standard value
- - necessary when comparisons are being made between pts, mm or sessions eg number of reps, exercises you do etc
What are the types of normalisation?
- - maximal voluntary isometric contraction
- - a totally relaxed state of mm
- - a set submax task
- - a comparison of ones mm activity with another
What causes signal variability?
- - electrode placement
- - electrode size
- - inter- electrode distance
- - skin conductivity
- - mm mass/ anatomical variation
- - sampling rate
- - can vary up to 20% with no reason
- - motor unit recruitment
- - fatigue
- - ambient temp
What are the two purposes of biofeedback?
- -to increase a mm output or level of activity (uptrain)
- - to dcrease a mm output or level of activity (downtrain)
What would it be good for in the clinic?
- - motor impairment post CVA
- -relaxation of hyperactive mm
- - increasing mm recruitment
- - urinary incontinence- mm function
- - 2 cm apart
- - be aware pf adipose tissue and adj mm cross talk
- VOL - Volume
- 05S WORK - Work time in seconds
- 05S REST - Rest time in seconds
- 05 TRLS - Number of trials
- ABV FDBK - Above feedback / Below feedback / Continuous / OffON
- SDAT – Serial data on / off (off for us)
- WDE FLTA / NRW FLTA – Wide or narrow band filter for channel A (NRW for chest, abdominal, shoulder and WDE for legs, arms, pelvic area or face)ON CHB – on / off for the second channel
- WDE FLTB / NRW FLTB (as for channel A)
- ON FBIH – Feedback inhibit is when ChB is on and down training is being performed
- 30 CBTH – If ON FBIH is on then once CHB is above CHA the sound will stopTHR BRGH – This button is used to set the ratio of ChA over ChB
What would you like to do?
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