Influence of endurance training on energy intake, norepinephrine kinetics, and metabolic rate in older individuals.

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 less than .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 less than .01) after moderate endurance training, despite no changes in body composition.(ABSTRACT TRUNCATED AT 250 WORDS)