The ARTE index: Characterizing free‐living physical activity and indices of cardio‐metabolic health among postmenopausal women

Abstract

PurposeThe doubly‐labeled water (DLW) technique is the gold‐standard used to objectively measure free‐living activity energy expenditure (AEE), however; it does not account for differences in body size or locomotion economy. Whereas the physical activity level (PAL) index, calculated from the ratio of total energy expenditure (TEE) and resting energy expenditure (REE), is employed to adjust for body size – it also does not account for variance in energy expenditure attributed to locomotion economy. Alternatively, the activity‐related time equivalent (ARTE) circumvents the limitations of AEE and PAL. In the present work, DLW was used to compare AEE, PAL, and variations of the ARTE index among a cohort of postmenopausal women dichotomized above/below the 50th percentile of normative data for body fat%. Correlations of AEE, PAL, and ARTE to measures of cardio‐metabolic health including arterial elasticity, body fat% and cardiorespiratory fitness (V̇O2max) were also performed.MethodsNinety‐two, healthy postmenopausal women (65+/−4 years) were recruited to measure free‐living AEE over a 14‐day period using DLW. TEE was reduced by 10% to account for the thermogenesis of feeding whereas AEE was calculated by subtracting REE from adjusted‐TEE. PAL was calculated from the ratio of TEE/REE. ARTE4act was calculated by dividing AEE by the average energy expenditure of non‐graded walking, graded walking, stair climbing, and a carrying task. AEE divided by the average energy expenditure of non‐graded walking was used to calculate ARTEwalk. Arterial elasticity was performed using pulse contour analysis from the radial artery. Dual‐energy X‐ray absorptiometry was used to estimate body fat% whereas a modified‐Balke protocol was used to measure V̇O2max. Between‐group comparisons were performed using independent t‐tests and Pearson’s correlation were used to evaluate relationships.ResultsBetween‐group differences were not detected for AEE, PAL, or the ARTE4act. However, women with less percent body fat (i.e., < 50th percentile) exhibited greater activity as evidenced by the ARTEwalk (min·day−1) (255+/−154 vs. 193+/−130; p < 0.05). Though AEE and PAL did not correlate with any cardio‐metabolic variables, ARTE4act was related to arterial elasticity (r = 0.24) and V̇O2max (r = 0.27) while ARTEwalk was related to arterial elasticity (r = 0.27), body fat% (r = −0.24), and V̇O2max (r = 0.32).ConclusionsConsistent with the ARTEwalk, adjustments for energetic cost of non‐graded walking may improve the sensitivity of AEE for detecting differences in free‐living physical activity and parameters of cardio‐metabolic health – known to be critical for overall well‐being.Support or Funding InformationThis investigation was supported by the following grants from the National Institutes of Health: R01AG027084‐01, R01AG027084‐S, P30DK056336, P60DK079626, and UL1RR025777.