PURPOSE: To determine the validity of three physical activity monitors in assessing energy expenditure during treadmill walking in normal, overweight, and obese adults.
METHODS: Measurements were obtained on 42 men and women (17 men, 29.0 ± 10.1 y, 25.9 ± 4.9 kg/m2; 25 women, 34.8 ± 11.1 y, 24.5 ± 4.6 kg/m2). Body Mass Index (BMI) was calculated via weight (kg) divided by height (m) squared. Each participant completed a walking treadmill (TM) protocol (1.5-4.0 mph, 5 minute stages, 0.5 mph increments) while energy expenditure (EE) was measured via indirect calorimetry (IC; ParvoMedics, Salt Lake City, UT ). Three pedometers (Sportbrain (SB), Omron HJ-700IT-T54 (OM), and Kenz Lifecorder (LC)) were worn on the right side of the hip according to manufacturer specifications throughout the protocol. Participants were divided into three BMI categories: normal (n = 24, ≤ 24.9 kg/ m2), overweight (n = 11, 25 −29.9 kg/m2), and obese (n = 7, ≥ 30.0 kg/m2). Mixed between-within subjects analysis of variance was performed on difference scores (IC EE - pedometer EE) to determine which pedometer was most effective in assessing EE across BMI categories during each TM speed. Tukey post hoc tests were performed to determine between group differences.
RESULTS: Results showed that EE difference scores derived from all pedometers were significantly different for TM speeds ≥ 2.0 (2.0 mph, p < 0.001; 2.5 mph, p < 0.001; 3.0 mph, p < 0.001; 3.5 mph, p < 0.001; 4.0 mph, p < 0.001). The between subjects main effect of BMI category showed significant differences for speeds of 2.5 mph (p = 0.010), 3.5 mph (p = 0.028), and 4.0 mph (p = 0.033), with specific differences seen between the normal BMI and obese individuals. Finally, the interaction effect of EE difference scores x BMI category was significant at speeds ≥ 2.0 mph at the p < 0.01 level.
CONCLUSION: These results support previous findings showing erroneous EE estimates from pedometers. These data extend previous findings showing that pedometer EE estimates were not the same for all BMI categories. Therefore, caution should be utilized in estimating EE with physical activity monitors in adults with different body sizes.
This work was partially supported by a Career Development Award from the National Institute on Aging (K01AG025962)