Motion sensor accuracy under controlled and free-living conditions.

PURPOSE: Two studies were conducted to examine the concurrent accuracy of the Yamax SW-200 (YAM), Omron HJ-105 (OM), and Sportline 330 (SL) pedometers, as well as a CSA accelerometer.

METHODS: In study 1, motion sensor performance was evaluated against actual (observed) steps taken during 5-min bouts at five different treadmill speeds (54, 67, 80, 94, and 107 m x min) using a two-way repeated measures ANOVA (instrument x speed). Additionally, the direction and magnitude of motion sensor error was examined. In study 2, pedometer performance during 24 h of free-living was evaluated against the steps detected by the CSA criterion. The direction and magnitude of pedometer error was also examined in the free-living condition.

RESULTS: In study 1, the SL showed significant differences from actual steps taken at all treadmill speeds (P < 0.05). Further, the absolute value of percent error was greatest for the SL at all treadmill speeds. At the slowest treadmill speed (54 m x min), the absolute value of percent error increased for the YAM and OM. In study 2, only the SL detected fewer steps than the CSA criterion (P < 0.05). The YAM demonstrated the lowest absolute value of percent error under free-living conditions.

CONCLUSIONS: Different brands of motion sensors detect steps differently; therefore, caution must be used when comparing step counts between studies that have employed different brands of motion sensors. Taking into consideration the results of both studies and the initial walking test used for instrument screening purposes, it appears that, of the three pedometers tested, the YAM pedometer is most consistently accurate under both controlled and free-living conditions. Future research must consider presenting motion sensor accuracy in absolute terms so that the magnitude of error is not underestimated.