Fat and carbohydrate metabolism during exercise in elderly and
young subjects.
Sial, Shahid, Andrew R. Coggan, Richard Carroll, James Goodwin, Samuel
Klein.
Department of Internal Medicine, Washington University School of
Medicine, St. Louis, Missouri 63110 and Departments of Internal
Medicine and Anesthesiology, The University of Texas Medical Branch,
Galveston, Texas 77555
APStracts 3:0160E, 1996.
We evaluated the effect of aging on fat and carbohydrate metabolism
during moderate intensity exercise. Glycerol, FFA, and glucose rates
of appearance (Ra) in plasma and substrate oxidation were determined
during 60 min of cycle ergometer exercise in 6 elderly (73+/-2 yr)
and 6 young adults (26+/-2 yr), matched by gender and lean body mass.
The elderly group were studied during exercise performed at 56+/-3 %
of maximum oxygen uptake, whereas the young adults were studied
during exercise performed at the same absolute and at a similar
relative intensity as the elderly subjects. Mean fat oxidation during
exercise was 25%-35% lower in the elderly subjects than in the young
adults exercising at either the same absolute or similar relative
intensities (P<0.05). Mean carbohydrate oxidation in the elderly
group was 35% higher than the young adults exercising at the same
absolute intensity (P<0.001) but 40% lower than the young adults
exercising at the same relative intensity (P<0.001). Average FFA
Ra in the elderly subjects was 35% higher than in the young adults
exercising at the same absolute intensity (P<0.05) but 35% lower
than the young adults exercising at a similar relative intensity
(P<0.05). We conclude that fat oxidation is decreased while
carbohydrate oxidation is increased during moderate intensity
exercise in elderly men and women. The shift in substrate oxidation
was caused by age-related changes in skeletal muscle respiratory
capacity because lipolytic rates and free fatty acid availability
were not rate limiting in the older subjects.
Received 1 April 1996; accepted in final form 25 July 1996.
APS Manuscript Number E163-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996