The role of physical activity in the regulation of energy intake in older persons is presently unclear. We therefore examined the influence of endurance training on voluntary energy intake and the associated changes in resting metabolic rate (RMR) and norepinephrine (NE) kinetics in seven healthy (six men, one woman) older individuals (69.4 ± 2.2 years) under supervised living conditions. Energy intake was measured by covert assessment in a clinical research environment during: (1) a 10-day inpatient control period (no exercise); (2) a 10-day light exercise period (150 kcal per session, 3 times/wk); and (3) a 10-day moderate exercise period (300 kcal per session, 3 times/wk). RMR was determined after all three periods, and NE kinetics were assessed before and after training by infusions of tritiated NE ([3H]-NE). No significant change in energy intake was found between the control (2,378 ± 130 kcal/d) and light exercise (2,449 ± 104 kcal/d) periods, whereas energy intake increased 17% (P < .01) during moderate exercise (2,785 ± 161 kcal/d). Changes in RMR paralleled those of energy intake, as no differences were noted in RMR after control (1.03 ± 0.12 kcal/min) and light exercise periods (1.04 ± 0.12 kcal/min), but RMR increased 9% (1.13 ± 0.14 kcal/min, P < .01) after moderate endurance training, despite no changes in body composition. Fasting levels of arterialized NE increased after endurance training (206 ± 39 v 265 ± 79 pg/mL, P = .06), due to a 22% increase in NE appearance (0.54 ± 0.28 v 0.66 ± 0.27 μg/min, P = .06) and no change in NE clearance (2.4 ± 0.6 v 2.4 ± 0.6 L/min). We conclude that under controlled laboratory conditions, healthy non-obese older individuals increase voluntary energy intake in response to moderate endurance training, and this is associated with an increased RMR and heightened sympathetic nervous system activity. These results suggest that the normal processes that regulate energy intake in response to moderate exercise are fundamentally intact in non-obese older individuals.
All Science Journal Classification (ASJC) codes
- Endocrinology, Diabetes and Metabolism