Total daily energy expenditure (“total expenditure”) reflects daily energy needs and is a critical variable in human health and physiology, but its trajectory over the life course is poorly studied. We analyzed a large, diverse database of total expenditure measured by the doubly labeled water method for males and females aged 8 days to 95 years. Total expenditure increased with fat-free mass in a power-law manner, with four distinct life stages. Fat-free mass–adjusted expenditure accelerates rapidly in neonates to ~50% above adult values at ~1 year; declines slowly to adult levels by ~20 years; remains stable in adulthood (20 to 60 years), even during pregnancy; then declines in older adults. These changes shed light on human development and aging and should help shape nutrition and health strategies across the life span.

Background:Urbanization affects lifestyles in the developing world but no studies have assessed the impact on objectively measured physical activity in children and adolescents from sub-Saharan Africa.Purpose:To compare objectively measured habitual physical activity, sedentary time, and indices of adiposity in adolescents from rural and urban areas of Kenya.Methods:Physical activity and sedentary time were assessed by accelerometry for 5 consecutive days in 97 (50 female and 47 male) rural and 103 (52 female and 51 male) urban adolescents (mean age 13 ± 1 years). Body Mass Index (BMI) and BMI z-scores were used to assess adiposity.Results:Rural males spent more time in moderate-to-vigorous intensity physical activity (MVPA) compared with urban males (68 ± 22 vs. 50 ± 17 min, respectively; P < .001). Similarly, Rural females spent more time in MVPA compared with urban females (62 ± 20 vs. 37 ± 20 min, respectively; P < .001). Furthermore, there were significant differences in daily sedentary time between rural and urban subjects. Residence (rural vs. urban) significantly (P < .001) influenced BMI z-score (R2 = .46).Conclusion:Rural Kenyan adolescents are significantly more physically active (and less sedentary) and have lower indices of adiposity compared with urban adolescents and this is a likely refection of the impact of urbanization on lifestyle in Kenya.

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Background: The impact of accelerometer-related methodological decisions relating to the assessment of physical activity and sedentary time has not been conclusively determined in young children. Objectives: To determine the effects of epoch and cutoff points on the assessment of physical activity and sedentary time and to determine the accelerometer wear time required to achieve reliable accelerometer data in children. Design: Children were recruited from centres at Ghent, Glasgow, Gothenburg and Zaragoza. Methods: Physical activity was assessed for 1 week in 86 children (41 girls, 45 boys; mean age 7±2 years) by uniaxial accelerometry. The epoch was set at 15 s and reintegrated to 30 and 60 s. Time spent sedentary and in moderate and vigorous physical activity (MVPA) was assessed using a range of cutoff points. Number of days required to achieve 80% reliability was predicted using the Spearman-Brown Prophecy formula. Results: The Reilly cutoff points (o1100 counts per min (CPM)) indicated less sedentary time per day when comparing 15 vs 30 s and 15 vs 60 s epochs: 570 ± 91 vs 579 ± 93 min and 570 ± 91 vs 579 ± 94 min, respectively; Po0.05. Pate cutoff points (4420 counts per 15 s) reported more MVPA time per day compared with Sirard (890 counts per 15 s) and Puyau cutoff points (43200 counts per min) using 15 s epoch: 78 (4-197) min (median (range) vs 18 (1-80) min and 24 (1-100) min, respectively; Po0.001. Compliance with guidelines of at least 60 min MVPA was 84, 78 and 73% for Pate cutoff points using 15, 30 and 60 s epochs, respectively, but 0% for Sirard and Puyau cutoff points across epochs. The number of days required to achieve 80% reliability for CPM, sedentary and MVPA time was 7.4-8.5 days. Conclusion: Choice of epoch and cutoff point significantly influenced the classification of sedentary and MVPA time and observed compliance to the MVPA guidelines.