Biofeedback & RealTime Motion Capture

Biofeedback – What are the possibilities?

With the release of The MotionMonitor xGen, our inaugural blog shared some of the things you have been telling us regarding the state of motion capture software.  Biofeedback and its use to understand human movement was one topic with lots of interest.  In this blog we will explore the topic and user applications in more detail.

What is biofeedback?
A typical definition of Biofeedback is “a treatment in which patients learn to control bodily processes that are normally involuntary such as muscle tension, blood pressure, or heart rate.”  In today’s world of research this definition is way too narrow.  The common view probably, flows from early use of surface electromyography (sEMG) to treat disorders ranging from tension headache to joint dysfunction.  A more appropriate and generalized definition might be: “Biofeedback is a process in which any raw or processed data derived from human movement, or initiation of movement, is provided to the subject in a control feedback loop with the purpose of modifying that movement through a process of learning.” 

With this broader definition the concept of “biofeedback” can use more data to analyze and modify behavior in a wide array of areas that range from performance enhancement in sports to injury reduction in ergonomics to rehabilitation of musculoskeletal injuries and to the rehab and study of motor control systems.

Steven Lavender,PhD at The Ohio State University, in a NIOSH grant proposal that was designed to modify the lifting behavior of manual material handlers, drew on Learning Theory and existing research to explain elements that are necessary for biofeedback to be effective.  He noted that complex motor skills are best learned when experienced rather than demonstrated; include "transitional cues" associated with modification of the behavior; and provide knowledge of results in the form of objective data to determine if a positive behavioral change has occurred.  In his case, the transitional cues were an auditory signal whose pitch was a function of the moment being generated on the L5/S1 joint.  Not your typical biofeedback signal!

Biofeedback clearly has possibilities well beyond that narrow definition.

How is Biofeedback Being Used?
So, how is biofeedback being used in the context of this broader definition and what are the types of feedback being provided as transitional cues?  One example is from the field of ergonomics.  If, as Steve Lavender suggests, “transitional cues” are important for modifying complex motor skills, visual cues alone may actually hinder learning.  In this ergonomic application designed to reduce shoulder elevation, an auditory signal indicating “out of bounds” would be more useful as an alert for the subject to immediately “feel” the danger zone.  The visual “stop and go” while useful to the coach, is too distracting for the subject.

Rehabilitation is another area that benefits from a broader definition of biofeedback.  Ricardo Matias of Setubal Polytechnic Institute, in an article “Effectiveness of Three-Dimensional Kinematic Biofeedback on the Performance of Scapula-focused Exercises” ( demonstrated that the use of kinematic feedback was more effective in modifying behavior than sEMG based feedback during certain shoulder motions.  Essentially, his research showed that sEMG, while useful in getting subjects to activate particular muscles, did not necessarily result in the desired change of scapular motion.  However, by using kinematic data as feedback, subjects not only modified their movement but also activated the correct muscle combination.

James Thomas, PT, PhD and Peter Pidcoe, PT, PhD at Virginia Commonwealth University are analyzing “how real” virtual reality has to be in order to engage the subject.  In their virtual Dodge Ball game which encourages people with back pain to move, they have added tactile feedback in the form of vibrators to provide feedback to body segments that have been “hit” by the opposing team.  In this example, visual interaction, reward systems and tactile feedback are providing a deeper level of feedback and a more real virtual world.

In golf, the swing lasts a fraction of a second.  This is too little time to monitor visual feedback or indeed to even modify the swing while in progress.  However, providing immediate feedback in the form of auditory signals during the swing can provide information that aids learning.  For example, to achieve the desired amount of shoulder rotation (technically thoracic rotation) a small interval can be set as a targeted success tone.   If no tone is heard the golfer did not rotate far enough.  Two tones indicate that they have rotated too far as they pass thru the zone on the back swing and again on the downswing.  And one tone was just right indicating they reached the zone but did not over rotate.

Biofeedback has been widely used in motor control.  It has been used both as a rehabilitation tool in the case of stroke and as a tool to better understand motor control systems.  For example, reaching into an immersive display of virtual objects allows the subject to observe their hand movement in a virtual environment that cannot be reproduced in the real world. 

Using error augmentation and a representation of the hand with an immersive display, James Patton, PhD at Rehab Institute of Chicago, displayed a perturbated representation of the hand which induces the subject to overcompensate as part of stroke rehabilitation protocol.  Using a similar display, Jill Campbell Stewart, PhD writing in Experimental Brain Research ( observed repeated reaches to random targets to discern the level of planning and compensatory adjustments undertaken by stroke patients.

Another application where visuals can be useful is during training. Using biofeedback with therapists as they learn manual therapy mobilization techniques is one example.  In this excerpt from a demo video, various visual representations can be used to monitor the amount of force that the therapist is applying.  Here a slip graph and bar graph are being used to ensure force is reaching the targeted level.

Of course, there are many other examples of biofeedback applications and research such as gait retraining, augmenting running mechanics, movement sonification and more. We encourage you to write to us at or in the comments below with your suggestions & questions for biofeedback applications. 

What is necessary for biofeedback software to be effective?
For software to be effective as a biofeedback tool there are two important considerations.  The first is speed of processing and latency in the display of feedback.  Measurement rates and software architecture are extremely important for biofeedback.  Processing speed must be sufficiently fast to eliminate latency between action and feedback for the training to be beneficial.  At the same time, the underlying collection rate has to be fast enough to satisfy Nyquist if the data were to be valid.  We discussed these issues in some detail in our 7/24/2018 blog on Real Time Collection of Biomechanical Data ( and should be reviewed carefully before investing in a biofeedback system.

The second consideration is the User Interface and ease with which biofeedback exercises can be constructed.  Subject deficiencies and the variety of research studies suggest that the user must be able to set up exercises quickly.  When investigating systems for use in biofeedback, this is arguably one of the most important issues.  If one is required to program or write exercises using Visual Basic or other programming languages, the setup time and limited interface will interfere with the successful use of biofeedback. 

We'd welcome the opportunity to talk with you about your applications & experiences with biofeedback. Feel free to use the comments section below or send us an email at


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