Using accelerometer and gyroscopic measures to quantify postural stability
Alberts JL, Hirsch JR, Koop MM, Schindler DD, Kana DE, Linder SM, Campbell S, Thota AK. Journal of Athletic Training 2015;50(6):578–588.
Take Home Message: Tablet hardware provided accurate data to quantify postural stability within 2.9° of data generated from a force platform system.
Postural instability deficits are frequently reported following a concussion. The balance errors scoring system (BESS) is a commonly used postural stability assessment; however, there are some limitations to its clinical utility (for example, its consistency between clinicians is low). Force platforms and 3-dimensional motion capture systems (for example, NeuroCom) are a more accurate method to assess postural instability; but due to the high cost it is not readily available for most medical professionals. Therefore, the authors determined whether postural instability could be quantified accurately with data gathered by an accelerometer and gyroscope within a tablet. The authors compared the center-of-gravity anterior-posterior sway-area data derived from the tablet’s sensor with the output from a NeuroCom sensory organization test. Forty-nine healthy participants completed the 6-condition sensory organization test on the NeuroCom while wearing a custom-built belt that securely held the tablet at the sacrum (close to participant’s center of mass). Data from the tablet was used to generate an anterior-posterior center-of-gravity sway metric to compare with NeuroCom’s center-of-gravity sway data. The majority of the differences (95% of the differences) in center of gravity between the two devices ranged from -0.5 to 0.5 degrees in test condition 1 (stable surface, normal visual field) to -2.9 to 1.3 degrees in test condition 5 (unstable surface, eyes closed). The largest absolute difference between the two devices was 2.9 degrees but in the first 4 test conditions it was only 1.4 degrees. Additionally, the authors found that the center of gravity value predicted by the tablet was similar to the NeuroCom center of gravity measurements across all trials.
Clinically, there is a gap between inexpensive, subjective clinical tests and more expensive biomechanical measurement techniques. However, the authors’ found that postural stability can be quantified accurately in healthy adolescent and young adults using data from the accelerometer and gyroscope embedded within a tablet. Overall, the tablet consistently provided a measure similar to the NeuroCom’s system across all conditions. During condition 1 the tablet was able to detect very small balance movements. The largest mean measurement error was in test condition 5. Condition 6 is the most challenging condition (unstable surface, sway visual reference), and the average difference between the two devices was less than 1 degree sway. This demonstrates that the tablet was able to detect larger balance movements. However, further research needs to be done among patients with concussions and other injuries as well as to determine whether different types of tablets can also measure sway accurately. The tablet cannot replace biomechanical analysis, but with the widespread availability and continual advancement of tablet technology inertial measurement hardware provides an opportunity for medical professionals to transition these devices from expensive Words with Friends notebooks to affordable data collection devices. Before a clinician starts using any tablet or smartphone app to collect clinical measurements they should remember to test its accuracy and whether it consistently provides good measurements.
Questions for Discussion: Would you use a tablet device to detect balance following a concussion? Would a tablet be an affordable option for your athletic training room?
Written by: Jane McDevitt, PhD
Reviewed by: Jeff Driban