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Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, N1G 2W1; and Department of Medicine, McMaster University, Hamilton, Ontario L8N 3Z5, Canada
This study investigated whether increased
provision of oxidative substrate would reduce the reliance on
nonoxidative ATP production and/or increase power output during maximal
sprint exercise. The provision of oxidative substrate was increased at
the onset of exercise by the infusion of acetate (AC; increased resting
acetylcarnitine) or dichloroacetate [DCA; increased
acetylcarnitine and greater activation of pyruvate dehydrogeanse
(PDH-a)]. Subjects performed 10 s of maximal cycling on
an isokinetic ergometer on three occasions after either DCA, AC, or
saline (Con) infusion. Resting PDH-a with DCA was increased
significantly over AC and Con trials (3.58 ± 0.4 vs. 0.52 ± 0.1 and 0.74 ± 0.1 mmol · kg wet
muscle
1 · min1).
DCA and AC significantly increased resting acetyl-CoA (35.2 ± 4.4 and 22.7 ± 2.9 vs. 10.2 ± 1.3 µmol/kg dry muscle) and
acetylcarnitine (12.9 ± 1.4 and 11.0 ± 1.0 vs. 3.3 ± 0.6 mmol/kg dry muscle) over Con. Resting contents of phosphocreatine,
lactate, ATP, and glycolytic intermediates were not different among
trials. Average power output and total work done were not different
among the three 10-s sprint trials. Postexercise, PDH-a in AC
and Con trials had increased significantly but was still significantly
lower than in DCA trial. Acetyl-CoA did not increase in any trial,
whereas acetylcarnitine increased significantly only in DCA. Exercise
caused identical decreases in ATP and phosphocreatine and identical
increases in lactate, pyruvate, and glycolytic intermediates in all
trials. These data suggest that there is an inability to utilize extra oxidative substrate (from either stored acetylcarnitine or increased PDH-a) during exercise at this intensity, possibly because of O2 and/or metabolic limitations.
pyruvate dehydrogenase; phosphocreatine; lactate; oxidative phosphorylation; isokinetic cycling; pyruvate; oxygen
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