Biofeedback

Biofeedback uses sensors to show a person a bodily signal, such as heart rhythm or muscle activity, so they can learn to influence it.

What it is

Biofeedback, in which sensors show a person a bodily signal so they can learn to influence it, is both a learnable skill and a way of measuring the body [1]. Three professional bodies jointly define it as a process in which instruments measure activity such as heart function, breathing, muscle activity and skin temperature and feed that information back rapidly [1]. The aim is a change the person can eventually make without the instrument [1].

Heart-rate variability (HRV) biofeedback works with the fluctuation in the time intervals between adjacent heartbeats [2]. Electromyography (EMG) biofeedback measures the electrical activity of muscles, and respiratory biofeedback measures the rate and depth of breathing [3]. Newer systems use motion sensors worn on the body to feed back posture and movement [3]. Neurofeedback, which feeds back brain activity, is a related but distinct modality and is not the focus of this page [1].

Continuous glucose monitoring (CGM) uses a small disposable sensor, placed just under the skin of the upper arm or abdomen, that measures glucose in the interstitial fluid, the fluid between the body's cells, every few minutes for up to about two weeks [4][5]. Because glucose reaches that fluid from the blood, the readings lag behind blood glucose by several minutes when glucose is changing quickly, and precision is lower at very high and very low values [4][5]. CGM was developed for people with diabetes, and its use by people without diabetes is a recent extension [5]. Unlike the modalities above, it is not a signal a person practises changing, so this page regards CGM as a measurement rather than as a skill.

How it is proposed to work

Biofeedback is usually explained as a form of operant conditioning: a signal that moves in the desired direction acts as a reward, and repeated practice is proposed to make the new response habitual. A typical session sets a baseline; the person then experiments with breathing, attention or muscle relaxation while watching the signal, until the change can be produced without the display.

For HRV biofeedback, the mechanism most often proposed involves breathing rate. HRV reflects the influence on the heart of the autonomic nervous system, the part of the nervous system that regulates functions such as heart rate without conscious control. Each person has a resonance frequency, the breathing rate at which heart-rate oscillations are largest, typically close to six breaths per minute. Breathing at that rate is proposed to maximise respiratory sinus arrhythmia, the natural rise and fall of heart rate with each breath. Regular practice is proposed to strengthen the baroreflex, the reflex that stabilises blood pressure. A further hypothesis concerns the vagus nerve, which carries signals from the body to emotion-regulating regions of the brain.

For CGM, the route proposed is behavioural rather than physiological. One hypothesis is that seeing how a meal or a walk is followed by a change in glucose prompts a different choice the next time. How such feedback might work is not settled.

For EMG biofeedback, the suggested mechanism is simpler: seeing or hearing muscle activity in real time is proposed to help a person consciously recruit a weak muscle or relax an over-active one. Posture feedback extends the same principle to motion sensors, using vibration or a display to prompt a change of position. These are proposed mechanisms, not statements of what biofeedback achieves.

What it is used for

Biofeedback is used in two broad ways: as training, in which a person practises changing a signal until they can do it without the display, and as measurement, in which the signal is recorded to see how a person responds to something.

HRV biofeedback is practised as a course of guided slow breathing, with the person's own heart rhythm shown in real time, in settings concerned with stress, mood and self-regulation, and by people with no particular complaint who want to practise the skill.

EMG biofeedback is used in physiotherapy and rehabilitation, for example to re-educate muscle after knee surgery, after a stroke and in pelvic floor training. Respiratory biofeedback is used to practise slower and more even breathing, and body-worn motion sensors are used to feed back posture and movement during daily activity or exercise.

Continuous glucose monitoring is used by people with diabetes to see their glucose through the day.

Our own trials

Most of the therapies and technologies we work with are young as subjects of scientific study, and the published work on them changes from year to year. Rather than point to studies that may already be out of date, HarmoniQ Tech intends to evaluate each therapy in its own trials, to record what we find, and to adjust our methods and our own algorithms to those findings. Our trials have not yet begun. Until they have, we describe what each therapy is, how it is proposed to work and how we intend to use it, and we make no claim about what it achieves.

Safety and who should take care

Biofeedback is described as non-invasive; sensor tape can irritate skin [3]. Breathing too deeply during slow breathing can cause faintness or palpitations; practitioners advise shallower, smoother breaths [6]. Resonance-frequency assessment is not advised for people whose heart rhythm is set by a pacemaker, may be unsuitable where over-breathing compensates for blood acidity, as in some kidney disease, and is postponed in asthma, generalised anxiety disorder or low back pain until slow breathing is comfortable [6]. Biofeedback requires active participation, is not advised as the only approach for severe hypertension, and is used with care in acute psychiatric conditions [3]. CGM sensors sit under the skin, and skin reactions at the site are a recognised complication: most often redness, itching and hardening of the skin, and occasionally severe enough to stop use [7]. Both irritant and allergic reactions to the adhesive occur, and the full adhesive composition may not be disclosed in product labelling [4]. Constant access to glucose data could cause distress or drive over-restrictive eating or excessive exercise in some people; this is a caution, not an observed harm [5]. Speak to a clinician before starting, especially during pregnancy, with a pacemaker or other implanted device, epilepsy, a heart or breathing condition, an acute injury, a condition or medicine that affects blood glucose, or a history of disordered eating.

How HarmoniQ Tech uses this

Biofeedback is intended to be the measurement layer of our approach. We intend it to give a person real-time awareness of their physiological state, for example HRV, muscle activity and breathing, and the skill of influencing it. After five years of our own research, we have finalised the set of sensors we will use, and we will add new sensors as new findings and development allow. That research was spent evaluating sensors and how they integrate with one another, not on trials. The sensors used for each person will be chosen for that person's starting point and goals. Sessions would sit alongside photobiomodulation (PBM), the application of red or near-infrared light to tissue, and a proprioceptive vibration therapy in a step-by-step plan for recovery from injury or lifestyle change. Continuous physiological signals from sessions and daily life are intended to be the primary sensor input for the HarmoniQ guidance system (in development), which we are developing to turn sensor data into step-by-step lifestyle guidance. Continuous glucose monitoring is intended to be one of those signals. We intend it as a data source for the guidance system rather than as a skill a person practises, and we do not offer it for any specific disease. Its purpose in our approach is to help a person see how particular foods and meals relate to their own glucose responses. We intend the person to keep a food diary alongside the sensor readings, so that each meal can be set beside the response that followed it. We intend to read those responses over repeated meals rather than from single readings. From that pattern, the aim is a diet plan built around the meals to which that person's own glucose rise was consistently smaller. Glucose is one measure of a meal, not a verdict on it. We intend to relate the same readings to the person's exercise, so that diet and exercise can be shaped into one routine. Our aim for that routine is that the person comes to anticipate their own responses to meals, and that those responses become steadier over time. That is an aim we intend to measure, not a result we claim. The guidance system is designed to use those signals, alongside posture and movement measurements and therapy session logs, to measure how a person responds to lifestyle changes and to the other therapies, and to adjust its suggestions as they progress. It will not diagnose, prescribe or treat.