Answer to Question 1
Lactate can be recycled into glucose and then reused as an energy source. Muscles release lactate into the blood, where it is circulated to the liver and converted to glucose via gluconeogenesis. Glucose is released into the blood and then taken up by muscles and other tissues. The release of lactate from the muscles into the blood, and its subsequent conversion to glucose by the liver, is called the Cori cycle. The Cori cycle helps increase glucose availability during periods of intense exercise.
Answer to Question 2
Until recently, the accumulation of lactate (lactic acid) in muscles was thought to be the cause of muscle soreness. Although lactate build-up may be associated with acute muscle pain, it does not adequately explain muscle soreness that often lingers for days after a vigorous workout. Scientists now believe that delayed onset muscle soreness, which occurs up to 24 to 36 hours after exercise, may be caused by microscopic tears in muscles in response to new activities or working out with greater intensity. Tiny tears cause muscle inflammation, which in turn causes localized soreness. At the same time, muscle fibers become stronger and better able to resist tearing, and therefore better equipped at handling the same type of exercise in the future.
Though not responsible for muscle soreness, the accumulation of lactate and other intermediate metabolic products does create an acidic environment (a lower pH), which inhibits the activity of enzymes needed for glycolysis. This drop in pH causes muscle contractions to weaken, contributing even more to fatigue and often causing a burning sensation in muscles.
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