Validation of Measures by the Lifecorder EX Activity Monitor

The purpose of this study is to determine the validity of the Lifecorder EX activity monitor in calculating resting metabolic rate, counting steps taken at a variety of speeds, reporting energy expenditure across a range of intensities, and categorizing exercise intensity in descriptive units as light (1-3), moderate (4-6), and vigorous (7-9). Ten male (24.6 ± 5.3 years) and ten female (26.6 ± 5.1 years) recreationally active adults participated in this study. Height, weight, resting metabolic rate, and body composition were measured prior to performing treadmill exercise at 9 speeds (54, 67, 80, 94, 107, 121, 134, 147, 161 m•min^-1), while wearing a Lifecorder EX activity monitor on both the right and left hips. Walking stages were performed for four minutes and running stages were performed for six minutes. Each stage was followed by a two-minute rest period. Energy expenditure was determined by indirect calorimetry and steps were tallied using a hand counter. In a separate trial subjects wore the activity monitor for 24-hours and met the investigator for a 30-minute exercise session on a 400-meter rubberized track. Subjects were randomized into one of three groups: a 30-minute run, 30-minute walk, or three 10-minute walks. The device significantly undercounted steps at the two slowest speeds (92.0% of actual at 54 m•min^-1 and 98.9% of actual at 67 m•min^-1), but accurately reported steps at speeds ≥ 80 m•min^-1. Both gross and net caloric expenditure were overestimated at all tested speeds except walking at 134 m•min^-1. On average, the device underestimated resting metabolic rate by 11.4%. The relationship between accelerometer reported intensity units and measured MET requirement was also determined. The Lifecorder EX has step counting accuracy comparable to other activity monitors studied in the recent past. Although the device overestimated both gross and net caloric expenditure the intensity units offered can be beneficial for helping describe an individual's physical activity pattern. The underestimation of resting metabolic rate is comparable to the error seen in many resting metabolic rate equations.