Validation of the Kenz Lifecorder EX and ActiGraph GT1M accelerometers for walking and running in adults

Accelerometer-based activity monitors are commonly used by researchers and clinicians to assess physical activity. Recently, the Kenz Lifecorder EX (KL) and ActiGraph GT1M (AG) accelerometers have been made commercially available, but there is limited research on the validity of these devices. Therefore, we sought to validate step count, activity energy expenditure (EE), and total EE output from the KL and AG during treadmill walking and running. Ten male and 10 female participants performed 10 min treadmill walking and running trials, at speeds of 54, 80, 107, 134, 161, and 188 m.min(-1). Step counts were hand tallied by 2 observers, and indirect calorimetry was used to validate the accelerometers' estimates of EE. AG total EE was calculated using the Freedson equation. Analysis of variance (ANOVA) and Pearson's correlations were used to analyze the data. At the slowest walking speed, the AG and KL counted 64% +/- 15% and 92% +/- 6% of the observed steps, respectively. At all other treadmill speeds, both activity monitors undercounted, compared with observed steps, by <= 3%. The KL underestimated activity EE at faster running speeds (p < 0.01), overestimated total EE at some walking speeds, and underestimated total EE at some running speeds (p < 0.01). The Freedson equation inaccurately measured total EE at most walking and running speeds. The KL and the AG are moderately priced accelerometers that provide researchers and clinicians with accurate estimates of step counts and activity EE at most walking and running speeds.