EMG

the summation of the various (nerve and muscle) compound action potentials generated during a contraction

• Frequency range: 10 hz to 10 khz
• Amplitude: 10 uV to 30 mV (surface)

Because muscles consist of relatively unique fiber compositions, the EMG signal of each muscle is also unique

• 1. Location
• 2. Activity
• 3. Intrinsic Factors
• 4. Other factors

• Isometric - constant position (think metre, distance, position)
• Isotonic - constant force
• Isokinetic - constant speed

No, except for isometric

• number of fibers active
• ph
• blood flow
• fiber diameter
• location of active fibers
• tissue composition

• Cross talk
• Band pass and spatial filtering
• AP superposition

• Absolute value of raw EMG signal (Rectification) is summated (integrated) over a period of time
• It can be used in maximal voluntary contraction calculations

Signals are averaged over a set number of cycles to reduce noise and highlight signal of interest

biofeedback


 Used as a tool for re-education of a muscle that demonstrates either

­Limited volitional strength

­Excessive activity that the individual is not able to volitionally control

Needle (or fine wire) EMG

• Muscular component of neuromuscular junction (will also reveal information regarding status of motor nerve supplying muscle)
• Phasic properties of muscle during functional activity (Kinesiologic)

Surface EMG

• Neural component of the motor unit (motor nerve conduction studies)
• Phasic properties of muscle during functional activity (Kinesiologic)

The use of electronic instrumentation to provide feedback regarding physiological function for the purpose of increasing one’s awareness of the response and modify that response to a desired level

úEMG *

úBlood pressure

úVisceral/vasomotor responses

úElectroencephalograph (EEG)

úHeart rate

No electrical stimulation is applied to the patient – instead electrical signals from physiological activity is recorded

• Functions as an intrinsic feedback mechanism
• Opposed to extrinsic (vision, proprioception, somatosensory)
• No direct information is contained in EMG regarding force/torque

• speed of feedback response
• continuity
• sensitivity
• objectivity

LOOK THIS over - slide 25

úPlace wider apart to increase attenuation

úAs control is gained move closer together

úPlace closer initially to work on one specific muscle or area of muscle

úAs control is gained move farther apart

úTypically work to gain control of relaxation and then focus on recruitment

Patient must initially develop awareness of activity, then work to achieve control over relaxation



úExample : Low Back Pain

 Supine positioning – relaxation of ES

 Sitting position – maintain low level

 Sit-stand and then lifting activites

úElectrode placement – start with close placement

The evaluation of muscle activity in relation to the movement of the body segments

Mix of concentric & eccentric activity

úConcentric activity occurs in brief bursts – Power generation

 Starts the limb’s momentum going forward and then it turns off to save energy

úEccentric muscle activity is very energy efficient – Power absorption

 What type (fast twitch or slow twitch) of muscle would you expect to be contracting eccentrically?

* Note: In understanding muscle in regard to movement, activity will always lead the joint being moved