ELECTROMYOGRAPHY ELECTROMYOGRAPHY ( EMG)( EMG)

Nerve conduction velocity Nerve conduction velocity ( NCV)( NCV)

ElectromyographyElectromyography

Definition:Definition: Electromyography is the electrical recording of muscle Electromyography is the electrical recording of muscle activity by placing electrodes on the skin or inserting electrodactivity by placing electrodes on the skin or inserting electrodes es into muscle; it is usually used to discern abnormalities of muscinto muscle; it is usually used to discern abnormalities of muscle le excitation.excitation.

Indications of EMG:Indications of EMG:-- neuroneuro--muscular diseases diagnosismuscular diseases diagnosis-- in working medicine and in working medicine and ergometryergometry studies in order to studies in order to

measure the muscular force developed during physical exercisesmeasure the muscular force developed during physical exercises-- in sport medicine , in order to appreciate the force in sport medicine , in order to appreciate the force

developed by the muscle fiber and the onset of muscle fatigue.developed by the muscle fiber and the onset of muscle fatigue.

Background

The function of the muscle is to convert the chemical energy to The function of the muscle is to convert the chemical energy to mechanical energy. In mechanical energy. In sckeletalsckeletal muscles, contraction is started by muscles, contraction is started by the action potentials that come from the motor nerves. the action potentials that come from the motor nerves.

Each neuron from a motor nerve innervates several muscle Each neuron from a motor nerve innervates several muscle fibers.Thefibers.The combination of a motor neuron and all the muscle combination of a motor neuron and all the muscle fibers it innervates is called fibers it innervates is called motor motor unitunit.The.The size of the motor unit size of the motor unit is determined by the function of the muscle. Muscles that perforis determined by the function of the muscle. Muscles that perform m fine movements like moving fingers need a greater degree of fine movements like moving fingers need a greater degree of control from the brain and have small motor units. Muscles that control from the brain and have small motor units. Muscles that maintain posture , do not need the same degree of control, so thmaintain posture , do not need the same degree of control, so the e motor units are much larger. If one neuron is stimulated, all tmotor units are much larger. If one neuron is stimulated, all the he muscle fibers of its motor unit will contract.muscle fibers of its motor unit will contract.

When an increase in the strength of a muscle's contraction is When an increase in the strength of a muscle's contraction is necessary to perform a task, the brain increases the number of necessary to perform a task, the brain increases the number of simultaneously active motor unitssimultaneously active motor units within the muscle. This process within the muscle. This process is known as is known as motor unit recruitment.

Motor unitMotor unit

ElectromyographElectromyograph -- component partscomponent parts1.1.--electrodes: 2 main types electrodes: 2 main types –– surface/ skin electrodes surface/ skin electrodes

-- needle electrodes: hypodermic needles that are needle electrodes: hypodermic needles that are inserted into the investigated muscle( allow to pick up informatinserted into the investigated muscle( allow to pick up information about a ion about a single muscular fiber)single muscular fiber)

2. 2. ––a higha high--gain amplifier with selectivity for frequencies in the range of gain amplifier with selectivity for frequencies in the range of 10 to 10 to several 1000 cycles/sec. several 1000 cycles/sec.

3. 3. ––recording display: recording display: osciloscopeosciloscope, chart recorder, audio ; , chart recorder, audio ; 4.4.-- stimulating and detection system ( used in NCV).stimulating and detection system ( used in NCV).

Electromyographic technique

- The patient is lay down on the bed in rest ( every movement can disturb the measurement)

- The electrodes are put on the skin of the patient(some times with a gel for a better contact): exploratory electrode overlying the muscle and indifferent one near it.

- The electrodes are connected with the miograph with cables.- After we swich the recorder we’ll analyse the muscle activity during rest

and graded voluntary effort.

Normal EMGNormal EMG

-- At rest there is no At rest there is no spontaneous activity in the spontaneous activity in the skeletal muscle of normal skeletal muscle of normal individuals ( A) individuals ( A)

-- In case of minimal voluntary In case of minimal voluntary activity , a few motor units activity , a few motor units discharge: a few action discharge: a few action potentials are recorded potentials are recorded ––simple recording (B)simple recording (B)

-- In increasing voluntary effort , In increasing voluntary effort , more motor units discharge ( more motor units discharge ( recruitment of motor units ) : recruitment of motor units ) : a high number of action a high number of action potential are recorded ( the potential are recorded ( the potentials from different motor potentials from different motor unit can be differentiated) unit can be differentiated) --intermediary recording (C)intermediary recording (C)

B.

C.

Normal EMGNormal EMG

-- In case of very intense contractions, In case of very intense contractions, a very high number of potentials a very high number of potentials are recorded, with no possibility to are recorded, with no possibility to identify their sourceidentify their source -- interference interference pattern( D)pattern( D)

-- In case of maximal contractions, In case of maximal contractions, the potentials appear as a the potentials appear as a sinusoidal waves, because of the sinusoidal waves, because of the synchronous activity of spinal motor synchronous activity of spinal motor neuronsneurons –– Piper Piper rhytmrhytm ( E).( E).

MaterialsMaterials

-- computer with BIOPAC computer with BIOPAC softwaresoftware

-- 6 single use electrodes6 single use electrodes-- BIOPAC EMG cables BIOPAC EMG cables

SS2L:SS2L:-- red : positive +red : positive +-- white: negative white: negative ––-- black:groundblack:ground

-- electrode gelelectrode gel-- BIOPAC DAU (data BIOPAC DAU (data

acquisition unit)acquisition unit)-- MP150MP150

Objectives

-- to record and observe motor unit recruitment and to record and observe motor unit recruitment and incresedincresedpower of the skeletal muscle contraction;power of the skeletal muscle contraction;

-- to compare the EMG trace from the left/right armto compare the EMG trace from the left/right arm-- to compare isometric contractions with isotonic to compare isometric contractions with isotonic

contractions.contractions.-- to to analiyseanaliyse the activity of antagonistic muscles ( biceps the activity of antagonistic muscles ( biceps

/triceps muscle)/triceps muscle)-- to to inregistrateinregistrate integrated EMGintegrated EMG

1. The recording of motor unit recruitment and 1. The recording of motor unit recruitment and incresedincresed power of the skeletal power of the skeletal muscle contraction ( biceps muscle)muscle contraction ( biceps muscle)

The activity of antagonistic muscles ( biceps /triceps muscle)The activity of antagonistic muscles ( biceps /triceps muscle)The recording of integrated EMGThe recording of integrated EMG

The activity of antagonistic muscles ( biceps /triceps muscle)The activity of antagonistic muscles ( biceps /triceps muscle)The recording of integrated EMGThe recording of integrated EMG

Nerve conduction velocity( NCV)

The velocity of the nerve conduction can be The velocity of the nerve conduction can be calculated by measuring two different values:calculated by measuring two different values:

1. 1. -- distance between stimulus ( electrical stimulation distance between stimulus ( electrical stimulation of the nerve ) and the place where we record the of the nerve ) and the place where we record the muscular contraction.muscular contraction.

2. 2. –– time between the stimulus and the responsetime between the stimulus and the response

distancedistancevelocity = velocity = ----------------------------------------

timetime

UlnarUlnar nerve : nerve : normal value of NCV :normal value of NCV : 4545--60 m/sec60 m/sec( decreased NCV: neuropathies of ( decreased NCV: neuropathies of

different causesdifferent causes-- toxic, toxic, alchoholicalchoholic, diabetes , diabetes mellitus ; compression of the nerve at the wristmellitus ; compression of the nerve at the wrist--carpal tunnel syndrome)carpal tunnel syndrome)

Factors that influence of NCV:1.- age : NCV of infants = ½ of the NCV of adults.( Myelination is not complete at birth, and that’s why NCV increase over the first few years of life.)

2.- temperature : NCV decreases by several % for each centigradedegree drop in body temperature.

3.- nerve segment : proximal segments present higher values of NCV than distal ones.( In arms, NCV is higher than in legs)

4.- nerve perfusion : ischemia reduces NCV