Energy expenditure estimates of the Caltrac accelerometer for running, race walking, and stepping

Objective - To examine the accuracy of the Caltrac accelerometer for estimating energy expenditure (EE) during three exercise modes. Methods - A subset of 31 women (mean (SEM) age 22.6 (5) years) was selected from a training study comparing various physiological parameters during race walking, running, and stepping. Subjects each performed mode specific graded exercise tests to peak Vo₂. Regression equations for Vo₂ v heart rate (HR) were generated from each individual's test data. EE (kcal and kJ) was estimated for each Vo₂ value based on the respiratory exchange ratio, and kcal v HR regression equations were generated to predict EE from each subject's HR data (EE-HR). HR in the field was monitored by telemetry, and two Caltrac monitors, one set for EE and one to give counts, were attached to a belt over opposite hips. Results - EE-HR was not significantly different across exercise modes. Caltrac overestimated EE (P < 0.01) in runners (14%) and walkers (19%) but underestimated EE in steppers by about 10% (P = 0.12). Conclusions - The Caltrac is a reliable instrument but it did not accurately distinguish EE in running, race walking, or stepping in a group of young women.