Can someone please answer these 2 questions on lactic acid build-up during exercise?

Question

1.) What role does the athlete's cardiovascular fitness play in lactic acid buildup?
2.) What are the physiological factors that may alter the amount of lactic acid accumulation in the same athlete?
Please give your source.

Answer 1

Contrary to what you might think, it is not lactate (lactic acid) buildup that causes muscle pain after exercise. But onto your question. Athletes function at a higher metabolic rate than normal people, and have more efficient cardiac output and circulation in general. As a result, lactate (a product of aerobic respiration) becomes a part of the Cori Cycle. This is basically a way the body transforms lactate (a 3 carbon sugar) into a much more useable form, glucose (a 6 hexose). This reaction occurs in the liver, whereas lactate formation occurs in the muscle cells. So, improved circulation in athletes allows them more efficient use of their lactate by improved Cori Cycle function.

This pathway is heavily dependent on oxygen availability (and thus pH). Less availability of oxygen (quick need for a lot of energy, like a sprint) means that the muscle cells will use ANAEROBIC metabolism to get their energy. Formation of lactate is anaerobic.