Metabolomics/Applications/Nutrition/Lifestyle/Exercise

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=Web Sources=

Web Site 1
http://www.sport-fitness-advisor.com/energysystems.html

Sport Fitness Advisor. "Energy Systems in Sport & Exercise" Sporting Excellence Ltd.

=Article Sources=

Article 1
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1282711 B Essén and L Kaijser. "Regulation of glycolysis in intermittent exercise in man" J Physiol. 1978 August; 281: 499–511.

Reviewed by Sarah Taber

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Summary


Continuous exercise leads to a drastic drop in glycogen levels and a large accumulation of glucose-1-phosphate (Gl-1-P), lactate and malate. The presence of these metabolites in muscle indicates glycolysis has occurred. During intermittent exercise, however, these metabolite levels were not nearly as high when the muscle underwent the same work load. Therefore, glycolysis is performed at a slower rate during intermittent exercise compared to continuous. Factors that influence this phenomena may be a smaller amount of substrate is demanded or the increased use of other substrates, specifically lipids.

During the rest periods in the intermittent trials, oxygen stores had a chance to replenish themselves. More oxygen allows for aerobic reactions to take place, which releases ten times more energy than the energy yielded from lactate formation. Not as much glycogen is required if the aerobic reaction is producing substantially larger amount of energy. Continuous exercise is accompanied by greater accumulation of lactate in the muscle and greater utilization of the lactate during vigorous activity.

Another difference between the two methods of exercise is during intermittent exercise lipids contribute to 40% of the oxidative metabolism while during 5 minutes of continuous exercise at maximum work load oxidative metabolism can be covered by only carbohydrates. This says that more fat is burned in intermittent training, rather than relying on immediate energy in carbohydrates. This shift to lipid utilization may also result in the regulatory factors slowing the rate of glycolysis.

When work is performed ATP, CP, and citrate levels decrease to a greater extent during continuous exercise, which activates glycolysis. The rest periods in intermittent training where ATP, CP, and citrate are being replenished is enough to inhibit glycolysis so the overall rate is much lower than during continuous training. The increase in ATP during rest periods also slows glycolysis indirectly through retardation of the citric acid cycle activity. This happends because the isocitrate dehydrogenase step is inhibited, leading to higher levels of citrate. Another precursor for the high citrate levels in intermittent exercise is the production of acetyl-CoA from fatty acid oxidation.

Glucose-6-phosphate inhibits hexokinase and phosphorylase B and the finding that the greatest amount of glucose-6-phosphate is in the early phase, which finally returns to basal level after an hr of exercise, supports that these two enzymes and phosphorylation of glucose is inhibited in the early phase.

The hypotheses that intermittent exercise is accompanied by greater use of lipids for oxidation, less accumulation of lactate, less glycogen consumption in the early phase, as well as high levels of glucose-6-phosphate in the early phase are supported by the concentrations of these metabolites taken from muscle biopsies. The data is not perfect because metabolite levels can change within seconds before the muscle is abstracted and preserved in liquid nitrogen before testing, however, the data trend collected from several trial and test subjects support the original hypotheses.

Relevance to a Traditional Metabolism Course

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