Inertial measurement units worn on the dorsum of the foot and proximal to the ankle can provide valid slip recovery measures

Abstract

Background: Slips are a leading cause of injury among older adults. Slip recovery measures are often captured using optoelectronic motion capture (OMC) systems that can be costly and typically require a laboratory setting. Inertial measurement unit (IMU) systems show promise as a lower cost, portable, and wearable form of motion capture. Question: Can IMUs worn on the dorsum of the feet and proximal to the ankles be used to capture valid slip recovery measures? Methods: Thirty older adults (ages 65–80; 18 females) were exposed to a laboratory slip while wearing OMC markers, IMUs on the dorsum of the feet, and IMUs proximal to the ankles. To evaluate the concurrent validity of IMU-based slip recovery measures using the OMC-based measures as our standard, we determined whether the IMU-based slip recovery measures differed between falls and recoveries, and evaluated the strength of correlation between IMU-based measures and OMC. We also defined the difference between foot IMU-based and OMC-based slip recovery measures to be the system offset, and compared the system offset variance between participant-placed IMUs and researcher-placed IMUs. Results: All IMU-based and OMC-based slip recovery measures differed between falls and recoveries (p ≤ 0.008), and all IMU-based measures exhibited strong correlation (r ≥ 0.94) with OMC-based measures. The system offset variance was larger when foot IMUs were participant-placed than when researcher-placed for anterior-posterior slip distance (p = 0.032), but not other slip recovery measures (p ≥ 0.054). Significance: IMUs worn on the dorsum of the feet and proximal to the ankle can provide valid slip recovery measures in a laboratory setting. This includes IMUs placed by participants on the dorsum of the feet that might be needed for the long-term monitoring of these measures by participants outside the laboratory setting.