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.

This study examined the effect of 12 weeks of exercise training on daily physical activity in elderly humans. Training consisted of a weekly group session and an individual session with cardio- and weight-stack machines. A group of 15 subjects served as the exercise group [EXER mean age 59 (SD 4) years], and 7 subjects as the controls [CONT mean age 57 (SD 3) years]. Physical activity and physical fitness were measured before the start of training (T), at week 6 and week 12 (T0, T6, T12 respectively) in EXER, and at T0 and T12 in CONT. Physical activity over 14 days was measured using a tri-axial accelerometer and physical fitness was measured during an incremental exercise test. At T12, mean maximal power output had significantly increased in EXER compared to CONT 8 (SD 12) vs -5 (SD 9) W; P < 0.02] and mean submaximal heart rate (at 100 W) had reduced [-10 (SD 7) vs -2 (SD 6) beats x min(-1); P < 0.05]. No differences or changes in physical activity were observed between EXER and CONT. At T6, physical activity on training days was significantly higher than on non-training days (P < 0.001). When the accelerometer output of the training session was subtracted from the accelerometer output on training days, at T12 non-training physical activity was significantly lower than on non-training days (P < 0.004). Accelerometer output of the individual training session at T12 had significantly increased compared to T6 (P < 0.05), whereas, accelerometer output of the group training session had remained unchanged. In conclusion, in elderly subjects an exercise training programme of moderate intensity resulted in an improved physical fitness but had no effect on total daily physical activity. Training activity was compensated for by a decrease in non-training physical activity.

OBJECTIVE: To assess the relationship between the mean physical activity level (PAL) and the time spent on activities of three different intensity levels in an elderly population. Data was compared with previously obtained data from a group of younger adults. SUBJECTS: Fourteen elderly women and 14 elderly men (61 AE 4 y; 27AE 5 kgam 2 ; 33AE 7% body fat), and 14 young women and 16 young men (27 AE 5 y, 24AE 2 kgam 2 ). MEASUREMENTS: PAL was determined as average daily metabolic rate (ADMR) combined with a measurement of basal metabolic rate (BMR): PAL ADMRaBMR. ADMR was measured with the doubly labeled water method. BMR was measured with a ventilated hood system. Time spent on activity and activity intensity was measured by using a tri-axial accelerometer (7 Â 2 Â 0.8 cm, 30 g) over a 2 week interval. RESULTS: Mean PAL was 1.65 AE 0.14. PAL was inversely related to the percentage of time spent on low-intensity activity (lying, sitting and standing), r 70.43; P`0.05. Older subjects spent signi®cantly more time at these activities than 20 to 35-y-old subjects (82 AE 7% vs 65 AE 7%; P`0.0001). A signi®cant relation was not observed between PAL and the percentage of time spent on moderate (walking) or high (household activities, exercise and sports) intensity activity, or activity monitoring time (14.4 AE 1.2 haday). CONCLUSION: In the elderly, spending relatively more time on low-intensity activities affects the mean PAL negatively. To obtain a higher PAL does not necessarily imply high-intensity activities like sports. International Journal of Obesity (2001) 25, 935 ± 939

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This study examined the effect of training on physical activity and substrate utilization in the elderly. Before the start, in week 6 and week 12 (T0, T6 and T12) data on physical fitness, physical activity and substrate utilization were collected in the exercise (11 males, 11 females; 63 +/- 8yrs) and control group (6 males, 5 females; 59 +/- 4yrs). Physical activity was registered with a tri-axial accelerometer and substrate utilization was calculated from resting respiratory exchange ratio (RER) by indirect calorimetry. At T6 physical activity on training days was significantly higher than on non-training days (33.4 +/- 10.3 vs. 26.5 +/- 7.8 counts x min(-1); p<0.001). At T12, after adjusting for training activity, physical activity on training days was significantly lower than on non-training days (23.7 +/- 8.4 vs. 28.2 +/- 9.3 counts x min(-1); p<0.01). RER decreased significantly (0.02 +/- 0.03; p <0.05), indicating a relatively larger fat oxidation. Changes in RER were negatively correlated with pre-training RER. In conclusion, in elderly an increase in structured training (exercise) is compensated for by a corresponding decrease in non-training physical activity. Training increased relative fat utilization in elderly with a high pre-training RER, whereas elderly with a low pre-training RER decreased their relative fat utilization.