EMG Biofeedback

EMG Biofeedback for physiotherapy students

1. EMG BIOFEEDBACK

2. Feedback Feedback is a response to a process or activity According to Weiner, 1948, ‘feedback is a method of controlling a system by reinserting into it the results of its past performance’ Physiological feedback is a self-regulatory biological system in which the output or response affects the input either positively or negatively

3. Feedback Physiological feedback refers to intrinsic information. These include kinesthetic, visual, cutaneous, vestibular, and auditory signals. Feedback from some measuring instrument refers to extrinsic information Also referred to as biofeedback.

4. everyday forms of biofeedback

5. Positive Feedback Change in one direction causes further change in the same direction

6. Negative Feedback Change in one direction causes further change in the opposite direction

7. In Biofeedback… The information is detected, provided in an understandable way to the patient who can then, at their own initiation, use the information to achieve a measure of control over the same process. i.e. engaging the patient in a ”closed loop” learning, using feedback until enough development of his motor skills occurs, so that an “open loop“ movements can be achieved.

8. Physiologic signal Response by patient Physiologic signal Response by patient Detection and feedback Open Loop Closed Loop

9. you must have accurate feedback, of course

10. Requirements To be realistic and successful, three main elements are needed in order to enhance motor learning: Relevant Accurate Speed of information Most EMG biofeedback devices nowadays introduce 50 to 100 milli sec. delays before the signal can reach the ears or eyes of the patient

11. EMG Biofeedback EMG does not measure muscle contraction directly. EMG measures electrical activity associated with muscle contraction. Electrical activity of muscle measured in micro volts (1 volt = 1,000,000 µV)

12. EMG Biofeedback Advantages: Can be integrated with other therapeutic interventions An enhancer of the therapy Reduce patient’s reliance on the therapist Gain control without reliance on the therapist, and once gained, Maintain control without either the therapist or the machine.

13. Working A biofeedback loop. Here the forearm muscles are monitored to provide a visual readout to the user. The feedback loop is completed when the user alters her muscle tension to adjust the readout.

14. Working Two active electrodes One reference electrode

15. Differential Amplifier A differential amplifier is used as the first stage of processing. Its advantage is that the elements which are common in both the signal inputs are subtracted by this differential amplifier. Ambient noise is subtracted out at this very first stage.

16. Working - CMRR Ability of the differential amplifier to eliminate the common noise between active electrodes is called the common mode rejection ratio (CMRR) Two signals are fed to a differential amplifier which subtracts the signal of one active electrode from the other active electrode. Differential amplifier also uses reference electrode to compare the signals of the two active electrodes. This in effect cancels out or rejects any components that the two signals coming from the active electrodes have in common thus amplifying the difference between the signals.

17. Working - filtering EMG signals are in the range of 0 – 500 Hz Frequencies above 500 Hz is filtered out The dominant energy of the EMG signal is in the range of 50 – 150 Hz Motion artifacts in the range of 0 – 20 Hz Frequencies below 20 Hz are filtered by using a high pass filter

18. Working – Rectification & Integration Raw EMG activity in muscle is an alternating voltage - direction or polarity is constantly reversing Rectification is the summation of electrical activity. To determine the overall increase and decrease in electrical activity, deflection toward the negative pole must be flipped upward toward the positive pole The signal may then be integrated by measuring the area under the curve for a specified period. Integration forms the basis for quantification of EMG activity.

19. Cues Visual cues Meter read outs Flashing lights Oscilloscope Computer screens Auditory cues Changing tones Clicks

20. Features of the BF Devices Gain settings, low & high Sound Threshold

21. Gain settings On low gain settings the machine will require a greater signal before the output changes - in other words, it is less sensitive. Used for muscle recruitment. On higher gain settings, a small amount of EMG activity will be easily seen by the patient. Used for relaxation.

22. Sound Most EMG biofeedback devices offer an audible feedback in addition to the visual information the change in sound is such that the frequency of the ‘beeps’ increases with increased EMG activity.

23. Threshold Incorporation of a threshold system enables the patient targets to be set. The audible signal can be adjusted so that it will only be heard if the patient achieves a preset activity level. To achieve an increase in muscle activity, the threshold can be set so that the audible feedback only comes on when 50% of the scale has been achieved.

24. Equipment

25. Electrode Placement Silver Chloride construction judicious electrode placement electrode spacing Noise/ movement artefact active electrodes should be placed in parallel with the dominant muscle fibres

26. Uses Facilitate muscle contractions Promote increased motor recruitment Regain neuromuscular control Decrease muscle spasm Promote relaxation

27. Indications Stroke Spinal cord injury Improving muscle action Posture control Balance and mobility Trunk muscle re education Respiratory muscle control Incontinence

28. Contraindications If the patient is prohibited from moving the joint or isometric contractions, then BF should NOT be used Unhealed tendon grafts Avulsed tendons Third degree tears of muscle fibers Unstable fracture Injury to joint structure, ligaments, capsule, or articulating surface

29. Technique for Motor Recruitment Position pt., Explain to pt., Work in quiet area. Apply sensors to an area to demonstrate the desired A-V signal and activity. Adjust to the most sensitive level that picks up any MUAP that pt. can produce Instruct pt. to try to produce an A-V signal As voluntary muscle activity improves, the A-V signal will increase. Adjust the gain to decrease the sensitivity, so pt. must work harder to recruit more muscle units. As pt. masters in one position, change positions Document all parameters. Tx duration 30-60 min Clean up

30. Inhibition of Spasticity Goal: decrease undesirable muscle activity that may be interfering with functional movement. Eval. spasticity, Explain to pt., Apply sensors and demonstrate desired activity. Find the least sensitive setting that produces minimal A-V feedback Have pt relax, use techniques and have pt. lower the A-V signal. As the signal decreases, lower the shaping controls (gain), to a more sensitive level. As pt. relaxes better, continue to increase sensitivity Change positions

31. Pressure Biofeedback A simple device to provide feedback to ensure quality, and precision in exercise performance and testing. Monitors position of the low back and provides feedback when the abdominal muscles are not actively or effectively protecting the spine.  

32. References http://en.wikipedia.org/wiki/Biofeedback http://bme2.aut.ac.ir/~towhidkhah/MotorControl/Resources/EMG.pdf http://www.electrotherapy.org/modalities/biofeed.htm Low & Reed, Electrotherapy Explained, principle and Practice, 4 th edition, 2009, Elsevier, Jagmohan Singh, Textbook of Electrotherapy,1 st Edition, 2005, Jaypee Publications.