Energy expenditure at rest and during activities: A comparison between young and elderly women.

Energy expenditure at rest (resting metabolic rate, RMR) and during several activities was measured in 20 young (age 19-27 years) and 19 elderly (age 65-78 years) females. Fat-free mass (FFM) was estimated by means of a four compartment model which accounted for variability in water and bone mineral in the FFM. RMR was lower (P < 0.05) in the elderly (mean ± SE 3.55 ± 0.05 kJ/min) compared to the younger females (3.92 ± 0.09 kJ/min). However, after correction for differences in FFM between the groups, RMR was 3.71 ± 0.07 kJ/min and 3.77 ± 0.06 kJ/min for the elderly and young, respectively, and the difference was not significant. Energy expenditure (EE) during several activities, standing with arm movement, bicycling at 25 Watts, and walking at 3 km/h, were not different between the two groups. However, the physical activity ratios (PAR) for the activities were higher (P < 0.05) in the elderly (1.61 ± 0.03, 3.29 ± 0.07, 4.11 ± 0.16, respectively) than in the young (1.47 ± 0.03, 2.93 ± 0.05, 3.58 ± 0.14, respectively). EE due to physical activity alone (total EE minus RMR) was significantly higher for all activities in the elderly, except for walking at fixed speed of 3 km/h. After correction for the lower relative FFM in the elderly, differences between age groups disappeared. EE for walking 500 m at an individually selected speed was higher in the elderly, although they selected a lower walking speed. Differences between young and elderly decreased when step frequency was taken into account. It is concluded that EE due to physical activity in elderly women is higher than in younger females, but that the differences in EE due to physical activity are largely attributable to differences in body composition. © 1996 Wiley-Liss, Inc.