During power exercises such as sprinting
, when the rate of demand for energy is high, lactate is produced faster than the ability of the tissues to remove it, so lactate concentration begins to rise. This is a beneficial process, since the regeneration of NAD+
ensures that energy production is maintained and exercise can continue.
*During intense exercise, the respiratory chain cannot keep up with the amount of hydrogen atoms that join to form NADH. NAD+
is required to oxidize 3-phosphoglyceraldehyde
in order to maintain the production of anaerobic energy during glycolysis. During anaerobic glycolysis, NAD+
“frees up” when extra nonoxidized hydrogens combine with a pyruvate molecule and then form lactate. If this does not occur, glycolysis comes to a stop. However, there is lactate being continually formed at rest and during moderate exercise. This occurs due to the metabolism of red blood cells
that do not have mitochondria
and limitations resulting from enzyme activity that occurs in muscle fibers that contain a high glycolytic capacity.
*The increased lactate produced can be removed in a number of ways, including: Oxidation
by well-oxygenated muscle cells
. Pyruvate is then directly used to fuel the Krebs cycle
. Conversion to glucose
in the liver and release back into the circulation; If not released, the glucose can be used to build up the liver's glycogen
stores if they are empty.