Transcript Biofeedback
Biofeedback Jennifer L. Doherty-Restrepo Entry-level Athletic Training Education Program PET 4995: Therapeutic Modalities Biofeedback Electronic or electromechanical instruments that accurately measures, processes, and provides feedback via auditory or visual signals Used to help patient develop greater voluntary control of either Neuromuscular relaxation, or Muscle re-education following injury Role of Biofeedback Intrinsic feedback = movement Kinesthetic, visual, cutaneous, vestibular, and auditory signals Extrinsic feedback = knowledge Results presented verbally, mechanically, or electronically to indicate the outcome of some movement performance Role of Biofeedback Feedback is ongoing Occurs before, during, and after any motor or movement task Feedback from some measuring instrument which provides moment-tomoment information about a biologic function is referred to as biofeedback Role of Biofeedback Patient able to make appropriate, small changes in performance which are immediately noted and rewarded Eventually larger changes, or improvements, in performance can be accomplished Goal = train patient to perceive changes without the use of a biofeedback unit Biofeedback Instruments Measure electromyographic activity (EMG) indicating amount of electrical activity during muscle contraction Most common type of biofeedback used in athletic training EMG Biofeedback Nerve fiber conducts an impulse to the neuromuscular junction where acetylcholine binds to receptor sites on the sarcolemma inducing a depolarization of the muscle fiber Changes in electrochemical potential difference associated with depolarization can be detected by an electrode placed in close proximity Measuring Electrical Activity EMG does not measure muscle contraction directly Measures electrical activity associated with muscle contraction Units of measure are microvolts 1 volt = 1,000,000 µV EMG readings may be compared only when the same equipment is used for all readings Measuring Electrical Activity EMG biofeedback unit receives small amounts of electrical energy generated during muscle contraction (via the electrodes) Separates or filters electrical energy from other extraneous electrical activity on skin Amplifies the EMG electrical energy and converts it to some type of information which has meaning to the patient Meter, auditory signal, light display Anatomy of EMG Biofeedback EMG Electrodes Skin surface electrodes Some electrodes permanently attach to cable wires while others may snap onto the wire Some units include a set of three electrodes pre-placed on a velcro band which attaches to the skin EMG Electrodes Size of electrodes varies 4 mm diameter for small muscle activity 12.5 mm diameter for larger muscles Increasing the size of the electrode will not cause an increase in the amplitude of the signal Electrodes may be disposable or nondisposable Require some type of conducting gel EMG Electrode Placement Prepare skin by scrubbing with an alcohol-soaked prep pad Electrodes should be placed as near to the muscle being monitored as possible Electrodes should be parallel to the direction of the muscle fibers Spacing of the electrodes is critical to reduce extraneous electrical activity (noise) Separation and Amplification of EMG Activity 2 active electrodes 1 reference electrode Active electrodes pick up electrical activity from motor units firing in the muscles beneath the electrodes Separation and Amplification of EMG Activity Magnitude of the small voltages detected by each active electrode will differ with respect to the reference electrode Creates two separate signals Separation and Amplification of EMG Activity Two signals feed into a differential amplifier Subtracts the signal of one active electrode from the other active electrode Uses reference electrode to compare the signals of the two active electrodes Separation and Amplification of EMG Activity Cancels out, or rejects, common components (noise) of the two signals coming from the active electrodes Results in amplification of the difference between the signals Separation and Amplification of EMG Activity Ability of the differential amplifier to eliminate the common noise shared by the active electrodes is called the common mode rejection ratio (CMRR) Separation and Amplification of EMG Activity External noise may be reduced by using filters Sensitive to some incoming frequencies and less sensitive to others Amplifier will pick up frequencies produced by electrical activity in the muscle Converting EMG Activity to Meaningful Information After amplification and filtering, the EMG signal indicates true electrical or raw EMG activity in muscle Raw EMG is an alternating voltage Direction or polarity is constantly reversing Converting EMG Activity to Meaningful Information To determine the electrical activity in the muscle, all negative waves are flipped upward toward the positive pole This summation of electrical activity is referred to as rectification Converting EMG Activity to Meaningful Information The rectified EMG signal can be smoothed Eliminates the peaks and valleys which are produced with a changing electrical signal Converting EMG Activity to Meaningful Information Once smoothed, the EMG signal may be integrated by measuring the area under the curve for a specified period of time Integration forms the basis for quantifying EMG activity Converting EMG Activity to Meaningful Information Biofeedback units generally provide either visual or auditory feedback relative to the quantity of electrical activity Visual feedback uses lights, bars, or analogue or digital meters Auditory feedback uses increasing or decreasing tones, buzzing, beeping or clicking Setting Sensitivity Sensitivity may be set at… 1 µV, 10 µV, or 100 µV A high sensitivity means the biofeedback unit is sensitive enough to detect the smallest amounts of electrical activity Higher sensitivity levels should be used during relaxation training Lower sensitivity levels should be used during muscle re-education training Clinical Applications Muscle re-education Isometric contractions sustained for 6-10 sec Maximize feedback Tx time = 5-10 min Relaxation of muscle guarding/Pain control Concentrate on muscle relaxation Minimize feedback Change positions Indications: Muscle re-education Regaining neuromuscular control Increasing isometric/isotonic strength Relaxation of muscle spasm/guarding Pain reduction Psychological relaxation Contraindications: Any musculoskeletal condition in which a muscle contraction may exacerbate the condition Questions???