Validation of the Lifecorder EX Activity Monitor

Abstract

The accuracy of physical activity monitors must be determined before use as objective measuring tools in research. PURPOSE: To examine the accuracy of the Lifecorder EX activity monitor as a step counter, method of calculating resting metabolic rate (RMR), and in measuring energy expenditure (EE) during activity. METHODS: Ten males and 10 females had their RMR measured using indirect calorimetry (IC). Subjects then performed a 9-stage treadmill test at increasing speeds from 2 to 6 mph. Speeds were increased 0.5 mph at the end of each 4-min walking stage or 6-min running stage. A 2-min rest period was taken between each stage. Steps were hand tallied (HT) and EE was measured by IC during activity. Subjects wore 2 Lifecorders, one of each side of the waistband. RESULTS: There were no measurement differences between Lifecorders for any stage (P < 0.05). A difference in step counts between the Lifecorder and HT was found only at speeds of 2.0 mph (P = 0.006; mean difference = 32.3 ± 8.66 steps) and 2.5 mph (P = 0.002; mean difference = 7.35 ± 2.95 steps). These step differences reflect an undercounting of 8.4 and 1.7 percent for those speeds, respectively. The Lifecorder underestimated net and gross EE compared to IC at all treadmill speeds (P < 0.05) for both genders. The average difference in EE for all stages was 4.41 and 5.52 kcals for net and gross EE, respectively. The Lifecorder significantly underestimated RMR compared to IC for both genders (P < 0.001; mean difference = 194.22 ±145.48 kcals/day). CONCLUSION: The Lifecorder EX underestimated RMR for males and females and consistently underestimated EE for both genders during treadmill walking and running. Step counts were only inaccurate at slow walking speeds, but the level of undercounting steps was small in comparison to many previously investigated pedometers.