Biofeedback therapy is an instrument-based learning process that is based on “operant conditioning” (also called instrumental conditioning, which is a learning process where behaviors are modified through the association of stimuli with reinforcement or punishment) techniques. It is an evidence-based approach to improve the ability to modify involuntary processes consciously. Physical therapists use biofeedback to help refine a movement sequence or activation pattern to assist patients to achieve a goal. This technique involves using visual, physical, and/or auditory feedback to guide the patient to give their optimal performance. The ultimate purpose is that the patient gets to know his body signs and that he can control them consciously using biofeedback equipment, afterward even without.
Biofeedback has been used for more than sixty years in rehabilitation to facilitate normal movement patterns after injury. It is the technique of providing biological information to patients in real time that would otherwise be unknown. This information can sometimes be referred to as augmented or extrinsic feedback, that is feedback that provides the user with additional information, above and beyond the information that is naturally available to them as opposed to the sensory feedback that provides self-generated information to the user from various intrinsic sensory receptors.
Many different types of biofeedback methods and techniques are used in rehabilitation. The classification of biofeedback is as follows:
The Neuromuscular system is the neurological and musculoskeletal systems working together to produce movement and locomotion. The methods used to measure this system in rehabilitation include EMG biofeedback and real-time ultrasound imaging (RTUS) biofeedback.
EMG biofeedback – EMG biofeedback is a method of retraining muscle by creating new feedback systems as a result of the conversion of myoelectrical signals in the muscle into visual and auditory signals. EMG uses surface electrodes to detect a change in skeletal muscle activity, which is fed back to the user by a visual or auditory signal. EMG biofeedback can be used to either increase activity in weak or paretic muscles or it can be used to facilitate a reduction in tone in a spastic one. EMG biofeedback is useful in both musculoskeletal and neurological rehabilitation.
Clinical Application – EMG biofeedback can be used in a variety of cases. One such popular case is post-op ACL repair/reconstruction. EMG biofeedback can be used to train the quadriceps muscle and all other lower limb muscles to improve strength after the surgery. Though it is not widely used, there have been cases where patients have benefitted greatly from it.
Another extremely important application of EMG biofeedback is in cases of pregnancy. EMG biofeedback helps in the strengthening of women’s pelvic floor muscles to prevent pelvic floor prolapse. A study conducted in 2022 stated that a single trial of EMG biofeedback significantly improved pelvic floor contractions in women.
RTUS biofeedback – RTUS sends short pulses of ultrasound into the body and using reflections received from tissue interfaces, images of internal structures are produced thus RTUS is capable of giving immediate real-time visual feedback of muscle activity by allowing the user to directly see the muscle changing shape/length on a display.
Clinical Application – Reports suggest that RTUS used to provide visual biofeedback improves activation of the multifidus muscle in healthy subjects. RTUS has also been successfully used to provide visual feedback on pelvic floor muscle activation. Dietz et al showed that 32 of 56 women learned the correct activation of pelvic floor muscles with less than 5 minutes of RTUS biofeedback training.
The Cardiovascular system is one of the most important systems of the human body. Sometimes, individuals require cardiovascular rehabilitation to improve their physical well-being after recovering from a disease. Cardiovascular measures which can be used to provide real-time biofeedback include heart rate (HR) and heart rate variability (HRV).
Heart rate biofeedback – HR can be measured using a heart rate monitor or an electrocardiogram to deliver feedback to patients. HR biofeedback is a therapeutic approach that allows patients to control their HR using a direct representation of the numerical value of HR on a wearable device such as a watch or a handheld display. Early studies suggest that HR biofeedback could significantly lower mean HR and systolic blood pressure during treadmill exercise.
Clinical Application – HR biofeedback can be used in every cardiac rehabilitation condition. For example, post-operative coronary artery bypass graft surgery.
Heart rate variability (HRV) – HRV refers to the variability in the time between heartbeats. These variations in HR are regulated by the autonomic nervous system. HRV at the frequency of respiratory, refers to the increase in HR with inspiration and the decrease in HR with expiration. HRV is easily measured and relatively reliable and thus it has been used as an index to understand a person’s internal state. During HRV biofeedback, an individual is instructed to breathe at low frequencies. Breathing at low frequencies (or deep breathing) causes large oscillations in instantaneous heart rate, which synchronize with breathing rate.
Clinical Application – HRV can be used to reduce stress, reduce asthmatic episodes and also improve cardiac and lung capacity in athletes.
The Respiratory system can also be regulated through the usage of biofeedback. Respiratory biofeedback is delivered by measuring breathing using electrodes or sensors attached to the abdomen and by converting breathing to auditory and visual signals for the user. Teaching diaphragmatic breathing in patients with respiratory disease is the most common means of providing respiratory biofeedback. Reports suggest that biofeedback-assisted diaphragmatic breathing and systematic relaxation were equally as effective as propranolol in reducing the frequency, severity, and duration of migraine headaches after six months of treatment. Delk et al compared diaphragmatic excursion and EMG feedback of accessory muscle activity to a control intervention of temperature biofeedback combined with relaxation therapy in participants with cystic fibrosis. The results of this study revealed significant improvements in measures of lung function in the experimental group while the control group showed no change.
Clinical Application – Respiratory biofeedback has been shown to promote relaxation and calm down breathing.
Biomechanical biofeedback involves measurements of the movement, postural control, and forces produced by the body. Inertial sensors, force plates, electrometers, pressure biofeedback units, and camera-based systems are all measurement devices that can be used to provide biomechanical biofeedback.
Inertial sensors – Inertial sensing uses accelerometers and gyroscopes to estimate three-dimensional (3-D) kinematic information of a body segment, such as orientation, velocity, and gravitational force. An accelerometer measures acceleration and gravitational acceleration, while a gyroscope is used to measure angular velocity. These inertial sensor parameters are used as input to a feedback system that delivers a wide variety of forms of feedback to the user including, auditory, visual, and tactile signals. As a result of their small size and portability, inertial sensors have proven useful in movement and balance applications. Research has shown that sensor-based feedback can be used to modify movement or behavior. Breen et al used a biofeedback system that used a single accelerometer to correct neck posture in computer users. Crowell and colleagues found that individuals can use real-time feedback of tibial acceleration from an accelerometer to reduce loading on their lower extremities while running and they can maintain the reductions for at least ten minutes after the feedback is removed.
Force plate – Force plate systems measure the ground reaction force generated by the body and can be used to give feedback on balance, movement, and gait. The feedback is normally delivered by using the ground reaction forces as input to a visual display that changes with changes in force. Several investigators have used force plate biofeedback to improve symmetry in standing posture, weight-bearing status, or balance and to train awareness of movement. The efficacy of using a force platform biofeedback system to improve balance in CVA rehabilitation has been examined. Reports suggest that visual feedback training using a force plate system is an effective method to gain a symmetrical stance following CVA.
Electrogoniometry – Electrogoniometry allows measurement of joint kinematics during functional tasks and movements yielding real-time feedback to clinicians and patients. As the kinematics of the joint change feedback is delivered, usually via an auditory signal or visual display. Ceceli et al and Morris et al analyzed the effectiveness of providing kinematic biofeedback of the knee, using electrogoniometers compared with conventional physiotherapy in efforts to minimize genu recurvatum in participants who had a CVA. Ceceli et al found that participants who were provided with kinematic biofeedback showed a statistically significant decrease in the number of knee hyperextensions compared with those who had received conventional physiotherapy only.
Pressure biofeedback – A pressure biofeedback unit (PBU) is a tool developed to aid the retraining of muscle activity and can provide useful visual biofeedback during treatment. A PBU consists of an inflatable cushion that is connected to a pressure gauge, which displays feedback on muscle activity. These units are relatively inexpensive and this technique is more easily applied in the clinical setting in comparison to previously mentioned techniques. PBUs have been used to indicate correct contraction of the transversus abdominis muscle during the abdominal hollowing exercise.
Biofeedback is an excellent tool that can be used in the field of rehabilitation as it has been proven and actively tested for years. Individuals suffering from neuromuscular and cardiac conditions have benefitted greatly from these methods. The only drawback of biofeedback is the lack of statistical data to show its effectiveness. While the evidence to support the use of biofeedback in rehabilitation appears promising, there is however a lack of systematic reviews. Having said that, biofeedback is purely evidence-based and can be actively used in the field of neuromuscular, pulmonary, and cardiac rehabilitation.