Calorimetric Validation of the Caltrac® Accelerometer During Level Walking

Abstract

The primary purpose of this study was to compare the Caltrac^® accelerometer output with measured energy expenditure (Ee). Twenty-five volunteers (10 men, 15 women) walked on a level motor-driven treadmill at four different speeds (54, 81, 104, and 130 m·min⁻¹) with the Caltrac^® device affixed to the waistline. Each of the four experimental trials lasted eight minutes, and the testing was completed within an hour. During the test, oxygen consumption (V̇o₂) (in L·min⁻¹ and in mL·kg⁻¹·min⁻¹) and nonprotein respiratory exchange ratio were monitored by the Beckman Horizon metabolic cart. The accelerometer output at the end of each exercise bout was also monitored and subsequently divided by 8 to convert the readings to counts·min⁻¹. The mean V̇o₂ (L·min⁻¹) at steady state (ie, 6th–8th minutes of exercise) was converted to a caloric value. We obtained a moderate correlation coefficient (r) of .76 between the accelerometer output and the V̇o₂ (mL·kg⁻¹·min⁻¹) and a high correlation coefficient of .92 between the Ee and the accelerometer readings. The Caltrac^® accelerometer output (counts·min⁻¹) was significantly higher (p < .01) than the Ee (kcal·min⁻¹) at the four walking speeds. The difference between the accelerometer output and the Ee ranged from 13.3% to 52.9%. The data were further analyzed with linear, polynomial, multiple, and stepwise regression models. The results of the analyses revealed that the Caltrac^® accelerometer output is a valid predictor of Ee during level walking when the appropriate regression equation is used to adjust the values. Because the accelerometer device tends to overestimate Ee, the raw accelerometer readings should be applied with caution.