Dr. Freguson does not want to spend January in Michigan, but he refuses to say h

Question

Dr. Freguson does not want to spend January in Michigan, but he refuses to say he is afraid of the cold. Instead he says he is going to be doing "research" by driving a Corvette C7 racecar in the Rolex 24 hours of Daytona in Florida. This is a 24 hour race that tests the enduranc of both the driver and the car. Dr. Ferguson has a VO2max of 56ml/kg/min, a max heart rate of 187 bpm, and a lactate threshold at 70% max VO2 (RER was 1.0 at lactate threshold). Additionally, Dr. Ferguson ran 20 practice laps around the Daytona speedway where his average heart rate was 145 bpm. How should Dr. Ferguson train for this race to prevent fatigue? Discuss what his lactate threshold should be in relation to his in car heart rate? Please relate this to what fuel he should be primarily metabolizing (carbohydrates or fat).

Explanation / Answer

Lactate production is due to oxygen debt. Its production leads to fatigue or muscle pain. Hence, sufficient intake of oxygen can reverse the effect of lactate.

Lactate production takes place in anaerobic condition from glycolysis (glucose breakdown, Pyruvate to Lactate in the presence of Lactate dehydrogenase enzyme) in skeletal muscle and heart that can be considered as a toxic byproduct. It can be re-shuttle into pyruvate in the liver by LDH in Cori-cycle and that acts as a precursor for gluconeogenesis and substrates for oxidation.

During physical exertion or moderate intensity exercise lactate released from working muscle and other tissue beds is the primary fuel source for the heart, exiting the muscles through monocarboxylate transport protein (MCT).

lactate is disposed of mainly through oxidation and only a minor fraction supports gluconeogenesis, lactate is the main gluconeogenic precursor during sustained exercise.

There will be a little difference in lactate production rates between trained and untrained subjects at equivalent power outputs. But there will be more efficient clearance rates of lactate in the trained subjects due to upregulation of MCT protein. Local lactate use depends on exercise exertion. During rest, approximately 50% of lactate disposal take place through lactate oxidation whereas in time of strenuous exercise (50-75% VO2 max) approximately 75-80% of lactate is used by the active cell, indicating lactate’s role as a major contributor to energy conversion during increased exercise exertion.

At last, Carbohydrates being the primary source of fuel energy since lactate is the product of glucose metabolism

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