Lipid fuel during exercise

Inherited aldolase A deficiency and pyruvate kinase deficiency in erythrocytes cause hemolytic anemia. The exercise capacity of patients with muscle phos-phofiaictokinase deficiency is low, particularly on high-carbohydrate diets. By providing an alternative lipid fuel, eg, during starvation, when blood free fatty acids and ketone bodies are increased, work capacity is improved. 

The observation of possibly increased IMCL levels in highly trained athletes led to a second focus of research in the field of sports medicine. Besides carbohydrates, lipids are the major fuel of skeletal muscle during work and rest. A variety of questions have to be answered. It was examined, whether exercise of various intensities alters IMCL levels, whether those changes depend on the duration of exercise, and finally, how IMCL are replenished during post-exercise recovery. 

During the early minutes of exercise, carbohydrate (plasma glucose and muscle glycogen) is the predominant fuel for the working muscles. When the exercise is prolonged and intensive, carbohydrate remains a predominant fuel with lipids (plasma free fatty acids and muscle triglycerides) being of lesser importance. When the exercise is of moderate intensity, lipids eventually become the primary fuel as carbohydrate stores are reduced. 

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