Accuracy of a custom-designed activity monitor: implications for diabetic foot ulcer healing

The relationship between repetitive trauma and propensity for ulceration and ulcer healing is unknown in part because of the lack of accurate information on activity level. The Step Activity Monitor (SAM) is a newly designed accelerometer to record activity level, but its accuracy is questionable. The purpose of this study was to determine the accuracy of the SAM under varying footwear and walking surface conditions. Ten healthy subjects consented to walk over 530 m of flat ground and up and down two flights of stairs, while wearing an athletic shoe or a fiberglass total contact cast (TCC). The accelerometer, programmed for a subject's cadence and leg motion, was secured to the distal, lateral aspect of the right lower leg. Two observers using hand-held digital counters followed the subject and recorded steps taken with the right leg on all walking surfaces. With the use of a repeated measures analysis of variance (ANOVA), the SAM and hand-held digital counters similarly recorded steps taken, regardless of walking surface condition. While the SAM was highly accurate (94 to 96 percent), the percent error was greater (p = 0.007) for the stair-climbing condition with the use of the TCC because of two subjects using a step-to-gait pattern. Overall, the SAM is an accurate accelerometer that will accurately record activity level, even with the application of a TCC. However, its accuracy may vary with deviations from a normal gait pattern.