Biofeedback is the technique of using equipment to reveal to human beings some of their internal physiological events, normal and abnormal, in the form of visual and auditory signals in order to teach them to manipulate these otherwise involuntary or unfelt events by manipulating the displayed signals. The ultimate purpose is that the patient gets to know his own body signs and that he can control them consciously in first place using biofeedback equipment, afterwards even without.
Furthermore, neuromuscular training or biofeedback therapy is an instrument-based learning process that is based on “operand conditioning” techniques. The governing principal is that any behavior-be it a complex maneuver such as eating or a simple task such as muscle contraction-when reinforced its likelihood of being repeated and perfected increases several fold.
Different types of biofeedback
The practice of biofeedback has developed markedly over the last few years, and many different forms of feedback are currently employed in the clinical setting. The most commonly used forms of biofeedback therapy are:
- Electromyography (EMG), measures muscle tension
- Thermal biofeedback, measures skin temperature
- Neurofeedback/ electroencephalography (EEG), measures brain wave activity
- Electrodermography (EDG), measures skin electrical activity
- Heat Flux, measures the rate at which heat is being dissipated from body
- Pneumography, measures abdominal/chest movement when breathing
- Capnometer, measures end-tidal CO2
- Hemoencephalography, measures the differences in the color of light reflected back through the scalp based on the relative amount of oxygenated and unoxygenated blood in the brain
- Photoplethysmograph (PPG), measures peripheral blood flow, heart rate, and heart rate variability
The wide range of inputs means that many applications can be developed from the existing equipment. The limits to biofeedback applications are largely with the therapist. Given an understanding of the basic principles of the therapy in combination with a clinical understanding of the patients problem, there are many novel applications for the therapy. Given the limited scope of this document, the following consideration will focus exclusively on EMG Biofeedback.
Mechanism of Action
The autonomic nervous system regulates the functioning of the organs and functions of the body like breathing and heart beating. It isn’t dominated by our will, but it reacts to our mood. There are two major components of the autonomic nervous system, the sympathetic and the parasympathetic systems. The parasympathetic works in particular at rest and recuperation while the sympathetic works at efforts. Due to chronic stress the autonomic nervous system can function worse, consequently the regulation of the body may get disrupted and an imbalance between the two systems may arise.
Biofeedback as a Component of Treatment
It is important at the outset to emphasize that biofeedback is not at its most effective when used as a treatment in its own right, but should be integrated with other therapeutic interventions. It acts as an enhancer of the therapy, enabling the patient (and the therapist) to make more effective and rapid progress towards the rehabilitation goal. Furthermore, it is useful in that it helps the patient to reduce their reliance on the therapist and become more reliant on their own performance. Clearly this is not fully achieved if the patient becomes reliant on the machine instead of the therapist! It can be used effectively to enable the patient to take some control or ownership over their rehabilitation - empowerment is an often used phrase in this context. The key to success of biofeedback in rehabilitation is to use the device as an adjunct to therapy, to enable the patient to gain control without reliance on the therapist, and once gained, to maintain control without either the therapist or the machine. This approach is entirely in keeping with the general aim of modern physiotherapy, and the technology is an aid to the outcome, not a magical solution.
EMG Biofeedback - Physiological Principles
The principles of EMG biofeedback (EMGBF) are usefully reviewed, as a reasonable understanding of what the machine is doing will assist the therapist in determining the most appropriate machine settings and applications.
Read more about the Physiological principles
There are many indications for biofeedback. Stress urinary incontinence is an indication for biofeedback. We found in the literature that the addition of biofeedback to the training of the pelvic floor muscles for the treatment of stress urinary incontinence improved pelvic floor muscles function, reduced urinary symptoms, and improved of the quality of life.
Pelvic floor muscle exercises and biofeedback are also an effective treatment for men with erectile dysfunction.
Further we found that EMG therapy is useful in enhancing knee extension after an ACL reconstruction but only in the early phase of the rehabilitation after the reconstruction.
If we search evidence for biofeedback as the treatment for headaches we found that biofeedback-related approaches to headache therapy fall into two broad categories: general biofeedback techniques (often augmented by relaxation-based strategies) and methods linked more directly to the pathophysiology underlying headache. 
The use of general biofeedback-assisted relaxation techniques for headache has been evaluated extensively. We can conclude that:
- various forms of biofeedback are effective for migraine and tension-type headache;
- outcomes with biofeedback rival outcomes with medication therapy;
- combining biofeedback with medication can enhance outcomes;
- despite efﬁcacy in many patients, biofeedback fails to bring signiﬁcant relief to a sizeable number of headache patients. 
Biofeedback methods that more directly target headache pathophysiology have focused chieﬂy on migraine and tension-type headache. These headache-speciﬁc approaches include blood volume pulse biofeedback, which has considerable supportive evidence, and electroencephalographic feedback. For tension-type headache we found that biofeedback was more effective than headache monitoring, placebo, and relaxation therapies. The strongest improvements were found for frequency of headache episodes. Further significant effects were observed for muscle tension.  Biofeedback is also used for patients with migraine. This treatment is found effective to reduce the number of headaches per week but there were no change in intensity, disability and length of headache. 
Other indications for biofeedback are:
- CVA 
- Chronic pain
- Neck pain
- Post traumatic stress syndrome
- Headache – migraine – tension headache
- Balance disorders
- Attention Deficit Hyperactivity Disorder
Features of the EMG Devices
- Gain settings
- Peak Hold facility
- Basmajian J. Biofeedback: Principles and Practices for Clinicians, Williams & Wilkins ,1989
- Biofeedback Vereniging Nederland. What is biofeedback? Available from: http://www.biofeedbackvereniging.nl/index.html (accessed 1/05/2013)
- Satish S.C. Rao. Dyssynergic Defecation & Biofeedback Therapy. Gastroenterology Clinics of North America, Volume 37, Issue 3, Pages 569-586, September 2009 (level 2A) Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2575098/
- University of Maryland Medical Center. Biofeedback 2011. Available from: http://www.umm.edu/altmed/articles/biofeedback-000349.htm (accessed 1/05/2013)
- Lockheed M. Biofeedback research report 2010. Available from: http://www.etc.cmu.edu/projects/lm-motion/Research/biofeedbackResearch.pdf (accessed 1/05/2013)
- Van Ark A. Biofeedback 2010. Available from: http://www.vabs.nl/biofeedback/wat-is-biofeedback (accessed 1/05/2013)
- Fitz FF, Resende AP, et al., Effect the adding of biofeedback to the training of the pelvic floor muscles to treatment of stress urinary incontinence , Revista Brasileira Ginecologia Obstetricia, November 2012 (level 2b)
- Norton C. Anal sphincter biofeedback and pelvic floor exercises for faecal incontinence in adults-a systematic review, Aliment Pharmacol Therapy 2001; 15(8), p1147-1154
- Dorey G, Speakman M, et al., Randomised controlled trial of pelvic floor muscle exercises and manometric biofeedback for erectile dysfunction, The British Journal of General Practice, November 2004 (level 1B)
- Christanell F, Hoser C, et al., The influence of electromyographic biofeedback therapy on knee extension following anterior cruciate ligament reconstruction: a randomized controlled trial, Sports Medicine Arthroscopy Rehabilitation Therapy & Technology, November 2012 (level 1B)
- Andrasik F. Biofeedback in headache: An overview of approaches and evidence, Cleveland Clinic Journal of Medicine, July 2010 (level 2A)
- Nestoriuc Y, Rief W, et al., Meta-analysis of biofeedback for tension-type headache: efficacy, specificity, and treatment moderators, Journal of Consulting Clinical Psychology, June 2008
- Budzynski T, Stoyva J, et al., EMG Biofeedback and Tension Headache: A Controlled Outcome Study, Psychosomatic Medicine, November 1973 (level 2B)
- Cohen M, Mcarthur D, et al., Comparison of Four Biofeedback Treatments for Migraine Headache: Physiological and Headache Variables, Psychosomatic Medicin, September 1980 (level 2B)
- Calomeni MR. Brain stimulation used as biofeedback training for recovery of motor functions deteriorated by stroke, Arq. Neuro-Psiquiatr 2013;71(3), p159-164,