biofeedback jennifer l. doherty-restrepo entry-level athletic training education program pet 4995:...

BiofeedbackBiofeedback

Jennifer L. Doherty-RestrepoJennifer L. Doherty-Restrepo

Entry-level Athletic Training Education ProgramEntry-level Athletic Training Education Program

PET 4995: Therapeutic ModalitiesPET 4995: Therapeutic Modalities

BiofeedbackBiofeedback

Electronic or electromechanical Electronic or electromechanical instruments that accurately measures, instruments that accurately measures, processes, and provides feedback via processes, and provides feedback via auditory or visual signalsauditory or visual signals

Used to help patient develop greater Used to help patient develop greater voluntary control of either voluntary control of either Neuromuscular relaxation, or Neuromuscular relaxation, or Muscle re-education following injury Muscle re-education following injury

Role of BiofeedbackRole of Biofeedback

IntrinsicIntrinsic feedback = movement feedback = movement Kinesthetic, visual, cutaneous, Kinesthetic, visual, cutaneous,

vestibular, and auditory signals vestibular, and auditory signals ExtrinsicExtrinsic feedback = knowledge feedback = knowledge

Results presented verbally, Results presented verbally, mechanically, or electronically to mechanically, or electronically to indicate the outcome of some indicate the outcome of some movement performance movement performance


Feedback is ongoingFeedback is ongoing Occurs before, during, and after any Occurs before, during, and after any

motor or movement taskmotor or movement task Feedback from some measuring Feedback from some measuring

instrument which provides moment-instrument which provides moment-to-moment information about a to-moment information about a biologic function is referred to as biologic function is referred to as biofeedbackbiofeedback


Patient able to make appropriate, Patient able to make appropriate, small changes in performance which small changes in performance which are immediately noted and rewardedare immediately noted and rewarded

Eventually larger changes, or Eventually larger changes, or improvements, in performance can improvements, in performance can be accomplishedbe accomplished

Goal = train patient to perceive Goal = train patient to perceive changes without the use of a changes without the use of a biofeedback unitbiofeedback unit

Biofeedback InstrumentsBiofeedback Instruments

Measure Measure electromyographic activity electromyographic activity (EMG)(EMG) indicating amount of electrical indicating amount of electrical activity during muscle contractionactivity during muscle contraction

Most common type of biofeedback used Most common type of biofeedback used in athletic trainingin athletic training

EMG BiofeedbackEMG Biofeedback

Nerve fiber conducts an impulse to the neuromuscular Nerve fiber conducts an impulse to the neuromuscular junction where acetylcholine binds to receptor sites on the junction where acetylcholine binds to receptor sites on the sarcolemma inducing a depolarization of the muscle fiber sarcolemma inducing a depolarization of the muscle fiber

Changes in electrochemical potential difference associated Changes in electrochemical potential difference associated with depolarization can be detected by an electrode placed with depolarization can be detected by an electrode placed in close proximityin close proximity

Measuring Electrical ActivityMeasuring Electrical Activity

EMG does not measure muscle EMG does not measure muscle contraction directly contraction directly Measures electrical activity associated Measures electrical activity associated

with muscle contractionwith muscle contraction Units of measure are microvolts Units of measure are microvolts

1 volt = 1,000,000 µV1 volt = 1,000,000 µV EMG readings may be compared only EMG readings may be compared only

when the same equipment is used when the same equipment is used for all readingsfor all readings

Measuring Electrical ActivityMeasuring Electrical Activity

EMG biofeedback unit receives small EMG biofeedback unit receives small amounts of electrical energy generated amounts of electrical energy generated during muscle contraction (via the during muscle contraction (via the electrodes)electrodes)

Separates or filters electrical energy Separates or filters electrical energy from other extraneous electrical activity from other extraneous electrical activity on skinon skin

Amplifies the EMG electrical energy and Amplifies the EMG electrical energy and converts it to some type of information converts it to some type of information which has meaning to the patientwhich has meaning to the patient Meter, auditory signal, light displayMeter, auditory signal, light display

Anatomy of EMG BiofeedbackAnatomy of EMG Biofeedback

EMG ElectrodesEMG Electrodes Skin surface electrodesSkin surface electrodes Some electrodes permanently Some electrodes permanently

attach to cable wires while others attach to cable wires while others may snap onto the wire may snap onto the wire

Some units include a set of three Some units include a set of three electrodes pre-placed on a velcro electrodes pre-placed on a velcro band which attaches to the skinband which attaches to the skin

EMG ElectrodesEMG Electrodes Size of electrodes variesSize of electrodes varies

4 mm diameter for small muscle activity 4 mm diameter for small muscle activity 12.5 mm diameter for larger muscles12.5 mm diameter for larger muscles

Increasing the size of the electrode will Increasing the size of the electrode will not cause an increase in the amplitude of not cause an increase in the amplitude of the signalthe signal

Electrodes may be disposable or non-Electrodes may be disposable or non-disposable disposable

Require some type of conducting gelRequire some type of conducting gel

EMG Electrode PlacementEMG Electrode Placement Prepare skin by scrubbing with an Prepare skin by scrubbing with an

alcohol-soaked prep padalcohol-soaked prep pad Electrodes should be placed as near to Electrodes should be placed as near to

the muscle being monitored as possible the muscle being monitored as possible Electrodes should be Electrodes should be parallelparallel to the to the

direction of the muscle fibersdirection of the muscle fibers Spacing of the electrodes is critical to Spacing of the electrodes is critical to

reduce extraneous electrical activity reduce extraneous electrical activity (noise)(noise)

Separation and Amplification of Separation and Amplification of EMG ActivityEMG Activity

2 2 active electrodesactive electrodes 1 1 reference electrodereference electrode Active electrodes Active electrodes

pick up electrical pick up electrical activity from motor activity from motor units firing in the units firing in the muscles beneath muscles beneath the electrodesthe electrodes


Magnitude of the Magnitude of the small voltages small voltages detected by each detected by each active electrode active electrode will differ with will differ with respect to the respect to the reference electrode reference electrode

Creates two Creates two separate signals separate signals


Two signals feed into Two signals feed into a a differential amplifierdifferential amplifier

Subtracts the signal of Subtracts the signal of one active electrode one active electrode from the other active from the other active electrode electrode

Uses reference Uses reference electrode to compare electrode to compare the signals of the two the signals of the two active electrodes active electrodes


Cancels out, or Cancels out, or rejects, common rejects, common components (noise) components (noise) of the two signals of the two signals coming from the coming from the active electrodes active electrodes

Results in Results in amplification of the amplification of the differencedifference between between the signalsthe signals


Ability of the Ability of the differential amplifier differential amplifier to eliminate the to eliminate the common noise common noise shared by the active shared by the active electrodes is called electrodes is called the the common common mode rejection ratio mode rejection ratio (CMRR)(CMRR)


External noise may be External noise may be reduced by using reduced by using filtersfilters Sensitive to some Sensitive to some

incoming frequencies incoming frequencies and less sensitive to and less sensitive to others others

Amplifier will pick up Amplifier will pick up frequencies frequencies produced by electrical produced by electrical activity in the muscleactivity in the muscle

Converting EMG Activity to Converting EMG Activity to Meaningful InformationMeaningful Information

After amplification and filtering, the EMG signal After amplification and filtering, the EMG signal indicates true electrical or indicates true electrical or raw EMGraw EMG activity in activity in muscle muscle

Raw EMG is an alternating voltageRaw EMG is an alternating voltage Direction or polarity is constantly reversingDirection or polarity is constantly reversing


To determine the electrical activity in the muscle, To determine the electrical activity in the muscle, all negative waves are flipped upward toward the all negative waves are flipped upward toward the positive polepositive pole

This summation of electrical activity is referred to This summation of electrical activity is referred to asas rectificationrectification


The rectified EMG signal can be The rectified EMG signal can be smoothed smoothed Eliminates the peaks and valleys which are Eliminates the peaks and valleys which are

produced with a changing electrical signalproduced with a changing electrical signal


Once smoothed, the EMG signal may be Once smoothed, the EMG signal may be integratedintegrated by measuring the area under the curve by measuring the area under the curve for a specified period of timefor a specified period of time

Integration forms the basis for quantifying EMG Integration forms the basis for quantifying EMG activityactivity


Biofeedback units generally provide Biofeedback units generally provide either visual or auditory feedback either visual or auditory feedback relative to the quantity of electrical relative to the quantity of electrical activity activity

Visual feedback uses lights, bars, or Visual feedback uses lights, bars, or analogue or digital metersanalogue or digital meters

Auditory feedback uses increasing or Auditory feedback uses increasing or decreasing tones, buzzing, beeping decreasing tones, buzzing, beeping or clickingor clicking

Setting SensitivitySetting Sensitivity

Sensitivity may be set at…Sensitivity may be set at… 1 µV, 10 µV, or 100 µV1 µV, 10 µV, or 100 µV

A high sensitivity means the A high sensitivity means the biofeedback unit is sensitive enough biofeedback unit is sensitive enough to detect the smallest amounts of to detect the smallest amounts of electrical activity electrical activity Higher sensitivity levels should be used Higher sensitivity levels should be used

during relaxation training during relaxation training Lower sensitivity levels should be used Lower sensitivity levels should be used

during muscle re-education trainingduring muscle re-education training

Clinical ApplicationsClinical Applications

Muscle re-educationMuscle re-education Isometric contractions sustained for 6-10 secIsometric contractions sustained for 6-10 sec Maximize feedbackMaximize feedback Tx time = 5-10 minTx time = 5-10 min

Relaxation of muscle guarding/Pain Relaxation of muscle guarding/Pain controlcontrol Concentrate on muscle relaxationConcentrate on muscle relaxation Minimize feedbackMinimize feedback Change positionsChange positions

Indications:Indications: Muscle re-educationMuscle re-education Regaining neuromuscular controlRegaining neuromuscular control Increasing isometric/isotonic strengthIncreasing isometric/isotonic strength Relaxation of muscle spasm/guardingRelaxation of muscle spasm/guarding Pain reductionPain reduction Psychological relaxationPsychological relaxationContraindications:Contraindications: Any musculoskeletal condition in which a Any musculoskeletal condition in which a

muscle contraction may exacerbate the muscle contraction may exacerbate the conditioncondition

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biofeedback jennifer l. doherty-restrepo entry-level athletic training education program pet 4995:...

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