AJP - Cell Physiology, Vol 262, Issue 4 C975-C979, Copyright © 1992 by American Physiological Society
Effect of low glycogen on carbohydrate and energy metabolism in human muscle during exercise
M. K. Spencer, Z. Yan and A. Katz
Department of Kinesiology, University of Illinois, Urbana 61801.
The effect of preexercise muscle glycogen content on the metabolic
responses to exercise has been investigated. Seven men cycled at a work
load calculated to elicit 75% of maximal oxygen uptake [211 +/- 17 (SE) W]
on two occasions: 1) to fatigue (37.2 +/- 5.3 min) and 2) at the same work
load and for the same duration as the first. Biopsies were obtained from
the quadriceps femoris muscle before and after exercise. Before the first
experiment, muscle glycogen was lowered by exercise and diet, and before
the second experiment, muscle glycogen was elevated. In the low-glycogen
condition (LG), muscle glycogen decreased from 182 +/- 15 at rest to 7 +/-
4 mmol glucosyl units/kg dry wt at fatigue, while in the high-glycogen
condition (HG), glycogen decreased from 725 +/- 31 at rest to 353 +/- 53
mmol glucosyl units/kg dry wt at the end of exercise. Hexose monophosphates
were not increased after LG exercise but increased approximately fivefold
after HG exercise. Lactate increased more during HG exercise (LG = 16 +/-
5, HG = 61 +/- 7 mmol/kg dry wt; P less than or equal to 0.001), whereas
IMP increased more during LG (LG = 2.8 +/- 0.6, HG = 0.9 +/- 0.2 mmol/kg
dry wt; P less than or equal to 0.05). The increases in the sum of
tricarboxylic acid cycle intermediates (TCAI; citrate+malate+fumarate) and
acetylcarnitine (which is in equilibrium with acetyl CoA) were
significantly greater during HG exercise (P less than or equal to
0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
