Utilizing and Interpreting the Balance Scan

This article provides an in-depth overview of key considerations and recommendations for utilizing and interpreting the Balance Scan within the Sparta Movement Health Platform.

 

Balance Scan Results

Overview

Though the Sparta Movement Health Platform (SMHP) calculates and makes available many individual biometrics for single-leg balance (> 40), high-level results displaying a Balance value for each limb, Balance Asymmetry, and an overall Balance composite score are highlighted after each Balance Scan for simple explanation and interpretation. These measures most concisely and intuitively characterize an individual’s balance capabilities and can provide insight into movement health, function, performance, and risk. Higher values for Balance and a lower percentage of Balance Asymmetry reflect better balance and less asymmetry respectively, with more detailed guidelines provided for the interpretation of these biometrics based on their absolute and/or normalized results.

Primary Metrics and Results

Balance and Sway

Balance: overall balance capability

Derived from the most recent Balance Scan, Balance represents an individual’s overall balance capability. Higher scores indicate better balance capabilities, with typical values ranging between 40-60.

Values for each limb (Left, Right), as well as a composite total Balance score, are generated from the data collected during the Balance Scan utilizing machine learning (ML) models optimized to reliably assess an individual’s ability to remain steady and minimize motion while balancing on a single limb. Balance is assessed based on standard posturography methodologies evaluating Center of Pressure (CoP) motion or “sway,” visualized in the image above, with the sway paths representing the individual’s CoP movement during a balancing task on the force plate sensor [1]. Higher values for each limb and total Balance composite reflect less motion during balance tasks and better balance capabilities. 

Balance Asymmetry Tooltip

Balance Asymmetry: asymmetry of balance from side-to-side

Balance Asymmetry represents differences in balance capabilities from side to side. Higher values indicate greater asymmetry, with typical values ranging between 0-20%.

A single value for Balance Asymmetry is presented as a percentage of relative asymmetry based on the Balance value for each limb. An asymmetry value of 0% reflects maximum symmetry between limbs, with higher asymmetry values reflecting greater asymmetry between limbs. Balance Asymmetry provides both asymmetry magnitude (%) and direction (R/L) to enable accurate and intuitive limb asymmetry monitoring in both healthy and injured populations.

Balance Scan Utility

  • Baseline Balance Assessment or Screening
  • Physical Therapy/Rehabilitation Testing and Protocols
  • Performance/Risk Identification
  • Balance/Gait Disorder Evaluation/Research
  • Fall Risk Assessment
  • Neurological/Vestibular Disorder Evaluation/Research
  • Traumatic Brain Injury (TBI) Evaluation/Research 

Interpreting Balance Scan Results

An impairment in balance is a potential cause of concern and motivation for balance improvement intervention. Scan results should be interpreted within the context of the assessment, as underlying conditions that adversely affect balance are manifold:

  • Musculoskeletal injuries or deficits
  • Brain injuries & neurological disorders
  • Sensory disorders

Balance Signature and Results

Balance values are normalized using our expansive database to provide contextual interpretation (e.g. gender, age) based on an expanding set of real-world data. Values for Balance typically range between 40 and 60 (with a population average of 50), with higher values representing better balance capabilities. Impairments in balance capabilities can be identified and monitored over time by identifying low or atypical total Balance results and/or individual limb results. 

Atypical Asymmetry

Balance Asymmetry is displayed as a percentage of relative asymmetry based on the Balance value for each limb. Values for asymmetry typically range between 0% and 20% with higher asymmetry values reflecting greater asymmetry between limbs. Small variations in asymmetry are common in people subjected to repeated testing and are typically not significant. Also, some people may exhibit high asymmetry due to known non-correctable issues such as pre-existing injuries.

There are cases, however, where subjects are unknowingly compensating with a better side, and where high asymmetry may reveal opportunities to improve overall balance capabilities.  Context knowledge of the subject is therefore important in using asymmetry information. 

Balance Trends

Longitudinal trends are able to be visualized for individuals over time by selecting any metric of interest in the Cloud interface of the SMHP to provide additional contextual information for interpretation. Understanding where typical scores lie for high-level metrics, Balance (40-60) and Asymmetry (0-20%), and visualizing these metrics over time provides clinicians and practitioners with the ability to easily interpret and relay this information within the context of their environment.

Balance Exercise

Improving Balance using Metric Guidance

Some aspects of balance improvement guidance are common sense:

  • Better general fitness and muscle tone improve balance
  • Repetitive practice of response to balance challenges improves balance

Reliably assessing balance capabilities for individuals over time using the Balance Scan provides an accurate and objective way to evaluate improvements and declines in overall and extremity-specific balance capabilities throughout treatment and care.

Balance is a complex activity that involves many physiological systems. A simplified 3 component electro-mechanical system analogy can be helpful in understanding balance response and paths to improvement:

  • the mechanism: The musculoskeletal system that is responsible for interacting with the ground and the repositioning of mass. 
  • the sensors: vision, vestibular, and tactile systems that provide the signal feedback about the state of the body over time.
  • the controller: the brain and spinal cord that process feedback and guide responses. 

Balance improvement, then, can be characterized in terms of these different components:

  • mechanism improvement: Improvements in mass distribution, muscle tone, core strength, flexibility, muscle actuation, etc. can significantly affect how efficiently the body can transmit force or reposition mass.
  • sensor improvement: Improving the quality and quantity of feedback signal data, greatly improves the ability of the controller to efficiently do its job. Likewise, any sensor deficit can handicap control.
  • controller improvement: Sending more optimal commands to the mechanism is a guaranteed path to balance response improvement. In this case, the controller is executing multiple strategies in parallel for managing coarse and fine-grained responses.

Improving Balance Capabilities

Balance can be enhanced by improving the mechanism of response (better force transmission and mass repositioning). 

  • Relative strength improvement
  • Flexibility improvement

Balance can be enhanced by improving coarse-grained control over balance response. 

  • Simple balance practice (e.g. knee lift, balance beam)

Balance can also be enhanced through repetitive practice at balance capability boundary exploration. Example exercise types include:

  • Balancing in the face of the following
  • Distracting tasks (dual-tasking)
  • Unexpected perturbations

Role of Asymmetry in Guidance

A high asymmetry that is deemed correctable can be addressed by choosing exercises that ensure that each side is equally worked - this can avoid the tendency for subjects to compensate with a more developed side over the other.

Users with Asymmetry values greater than or equal to 20% will be highlighted for further interpretation and guidance as these can be considered atypical results that warrant further investigation and potential intervention.

Other Metrics of Interest

control-mrv

Control - balance response or complexity 

Values for each limb (Left, Right) as well as a composite total score are generated from the data collected during the balance scan utilizing machine learning (ML) models optimized to reliably assess an individual’s ability to make complex adjustments to maintain balance in unpredictable conditions. Control is assessed based on standard methodologies for evaluating time-series signal complexity (e.g. entropy). 

Measurement of the ‘complexity’ of dynamic biometric physiological signals is an increasingly important assessment tool [2]. Heart rate variability (HRV) is familiar to many people, but other signals like respiration and EEG are also studied. In general, high complexity of response is associated with better health. Signal complexity is typically measured through sample entropy calculations. The intuition for Control is that higher complexity of response implies a better ability to make fine adjustments at different timescales in order to maintain stability in the face of unpredictable destabilizing perturbations [3].

Additional Resources

References

  1. Chen,B.;Liu,P.;Xiao,F.; Liu, Z.; Wang, Y. Review of the Upright Balance Assessment Based on the Force Plate. Int. J. Environ. Res. Public Health 2021, 18, 2696. https:// doi.org/10.3390/ijerph18052696
  2. Stergiou, N. (2016). Nonlinear Analysis for Human Movement Variability (1st ed.). CRC Press. https://doi.org/10.1201/9781315370651
  3. Manor B, Costa MD, Hu K, et al. Physiological complexity and system adaptability: evidence from postural control dynamics of older adults. J Appl Physiol (1985). 2010;109(6):1786-1791. doi:10.1152/japplphysiol.00390.2010