Determining optimal wearable sensor location for detection of differences in younger versus older adults.

Objectives: Previous studies have assessed the efficacy of wearable sensors in detecting differences between younger and older adults or non-fallers and fallers as a means for predicting fall risk in these populations. Numerous combinations of variables (e.g., acceleration, step length, stride duration, and harmonic ratio) have been measured using various sensor locations (e.g., iliac crest, sacrum, dorsal foot, femur, and shin). Currently, there is no consensus among researchers regarding the ideal sensor location for detecting significant differences in these variables between either younger and older adults or non-fallers and fallers. Therefore, the purpose of this study was to determine if common fall risk variables are able to detect differences in relatively healthy younger and older adults as a means for earlier-onset fall risk detection and determine optimal sensor location to make these measurements easier in a clinical setting. We hypothesized that older adults would demonstrate decreased average range of acceleration and the sacrum would be the optimal sensor location for detecting differences in acceleration because of its close proximity to the center of mass. Design: 12 participants voluntarily enrolled and were divided into 2 groups based on age (18-35 and >60 years). Subjects performed a 2-minute treadmill walking task at a self-selected habitual pace. Wearable sensors were placed on the sacrum, lateral femur, and anterior tibia bilaterally. Sensors measured linear acceleration in the anteroposterior (AP), mediolateral (ML), and vertical (V) directions. The average range of acceleration across 10 gait cycles was calculated for each subject. Results: No significant differences in acceleration were found between groups in the AP and V directions for sensors placed at the sacrum (p≥0.317) and lateral femur (p≥0.054) or in any direction for sensors placed at the anterior tibia (p≥0.395). ML acceleration was significantly decreased in the older adults group at the sacrum (Younger=8.83±1.05 m/s2, Older=7.09±1.09 m/s2; p=0.034) and the right lateral femur (Younger=37.58±17.00 m/s2, Older=27.33±4.85 m/s2; p=0.017). Conclusion: With the exception of ML acceleration, acceleration was not found to be significantly different between groups. Significant differences in ML acceleration measured at the sacrum and lateral femur are consistent with previous studies. Compared to AP and V acceleration, hip sway during walking as measured by ML acceleration is more prominent and easier to detect in a clinical setting. Greater side-to-side sway could correlate with instability and thus, an increased risk of falls. Therefore, ML acceleration may be an important variable to focus on in future studies emphasizing earlier fall risk detection in healthy adults. The results suggest sacrum and lateral thigh (rather than anterior tibia) sensors would be more advantageous at detecting differences in acceleration in such studies.