Lab 03-LT-Fall 07

Lab 03-LT-Fall 07 - Lab 3 Lactate Threshold Purpose The...

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Lab 3 – Lactate Threshold Purpose The purpose of this lab is to establish the VO 2 , work rate, ventilation rate, and heart rate at which point lactate begins to accumulate in the blood. Introduction One of the main functions of glycolysis is to convert a 6 carbon glucose molecule into two 3 carbon pyruvate molecules. These pyruvate molecules can either be converted into lactate or acetyl-CoA . Acetyl-CoA enters the TCA cycle and eventual leads to production of ATP while lactate is transported out of the cell and carried in the blood to other tissues where it is converted back into glucose. The conversion of pyruvate into acetyl-CoA is catalyzed by the multienzyme pyruvate dehydrogenase complex (PDC) attached to the outer mitochondrial membrane. This reaction requires the presence of oxygen ( aerobic conditions). The conversion of pyruvate into lactate is catalyzed by lactate dehydrogenase (LDH) . The conversion of pyruvate into lactate can be considered the default fate of pyruvate with the production of acetyl-CoA occurring only when sufficient oxygen is present. Since the PDC is attached to the mitochondrion, its presence in muscle can be quantified relative to the number of mitochondria à the more mitochondria, the more PDCs. Generally, during aerobic exercise of sufficient intensity, PDCs are activated and most of the pyruvate is converted to acetyl-CoA. The small amount of pyruvate that is converted to lactate exits the cell and circulates in the blood to other tissues. This small amount of lactate always present in the blood is the termed the basal or baseline plasma lactate concentration and is usually around 1.0 mmol. As exercise intensity increases, more pyruvate is made. This additional pyruvate continues to be converted into acetyl-CoA so long as there are enough “free” PDCs to accept it. Eventually, an exercise intensity is reached where all of the PDCs are “occupied” by pyruvate. Any increase in exercise intensity beyond this point (resulting
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This note was uploaded on 07/24/2008 for the course KIN 325K taught by Professor Dingwell during the Spring '07 term at University of Texas.

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Lab 03-LT-Fall 07 - Lab 3 Lactate Threshold Purpose The...

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