Accuracy of Two Measures of Weight-Bearing Activity in People with Prior Diabetic Foot Ulcers

Background/Purpose: The role of weight-bearing activity (WBA; i.e., standing and walking) in ulcer recurrence among persons with histories of diabetic foot ulcers (DFU) remains unclear because WBA has been measured in previous studies using either self-report, which is subjective, or pedometers, which fail to capture standing. Two activity monitors (Monitor 1 and 2) are available that allow the measurement of both standing and walking. The purpose of this study was to evaluate their accuracy among persons with previous DFUs.  

Methods: Thirty-one subjects with prior DFUs were enrolled. Subjects performed 14 standardized activities, including standing, sitting, lying down at different postures, and walking and stair climbing at different paces while wearing both monitors simultaneously. Subjects’ posture during each activity and number of steps taken were also measured using direct observation of video recordings. Paired t-tests were used to evaluate the accuracy between the two monitors and direct observation of each activity.  

Results: Monitor 1 showed 96.7%-100.0% accuracy rate for identifying postures for most of the activities, while the accuracy of Monitor 2 varied from 13.8% to 100.0 %. Steps recorded by Monitor 1 during regular walking and slow stair climbing, were not significantly different than observed measures (average difference 3-11 steps, p=.13-.29), while steps taken during other speeds of walking and stair climbing were statistically different (average difference 10-17 steps, p=.001-.004). Steps taken with Monitor 2 during all speeds of walking and stair climbing were significantly different than observed measures (average difference 34-73 steps, p<.001).

Conclusions: Overall, Monitor 1 demonstrated better accuracy than Monitor 2 for distinguishing postures and provides an accurate measure for standing. However, neither monitor demonstrated accuracy for walking. Based on our findings, we suggest Monitor 1 together with a valid pedometer can accurately and comprehensively measure both standing and walking to evaluate WBA in persons with DFUs.