Using Accelerometer and Gyroscopic Measures to Quantify Postural Stability

Context: Force platforms and 3-dimensional motion-capture systems provide an accurate method of quantifying postural stability. Substantial cost, space, time to administer, and need for trained personnel limit widespread use of biomechanical techniques in the assessment of postural stability in clinical or field environments. Objective: To determine whether accelerometer and gyroscope data sampled from a consumer electronics device (iPad2) provide sufficient resolution of center-of-gravity (COG) movements to accurately quantify postural stability in healthy young people. Design: Controlled laboratory study. Setting: Research laboratory in an academic medical center. Patients or Other Participants: A total of 49 healthy individuals (age = 19.5 +/- 3.1 years, height = 167.7 +/- 13.2 cm, mass = 68.5 +/- 17.5 kg). Intervention(s): Participants completed the NeuroCom Sensory Organization Test (SOT) with an iPad2 affixed at the sacral level. Main Outcome Measure(s): Primary outcomes were equilibrium scores from both systems and the time series of the angular displacement of the anteroposterior COG sway during each trial. A Bland-Altman assessment for agreement was used to compare equilibrium scores produced by the NeuroCom and iPad2 devices. Limits of agreement was defined as the mean bias (NeuroCom - iPad) +/- 2 standard deviations. Mean absolute percentage error and median difference between the NeuroCom and iPad2 measurements were used to evaluate how closely the real-time COG sway measured by the 2 systems tracked each other. Results: The limits between the 2 devices ranged from -0.5 degrees to 0.5 degrees in SOT condition 1 to -2.9 degrees to 1.3 degrees in SOT condition 5. The largest absolute value of the measurement error within the 95% confidence intervals for all conditions was 2.9 degrees. The mean absolute percentage error analysis indicated that the iPad2 tracked NeuroCom COG with an average error ranging from 5.87% to 10.42% of the NeuroCom measurement across SOT conditions. Conclusions: The iPad2 hardware provided data of sufficient precision and accuracy to quantify postural stability. Accuracy, portability, and affordability make using the iPad2 a reasonable approach for assessing postural stability in clinical and field environments.