Richard,
In the research that I have done, and I have so much because my thesis incorporated lactate metabolism. According to McLlroy (16), were the first to name anaerobic threshold to define a particular workload at which blood lactate levels first begin to rise above resting levels during a test to measure exercise tolerance. An increase in expired ventilation in milliliters per minute that was greater that the rate of on going increase in O2 uptake also began to occur. The term anaerobic threshold seemed logical to suggest the notion that the anaerobic metabolic process supplemented the aerobic process to provide energy for movement. The term anaerobic refers to region of change (2,16).
The literature that I have come across has never stated that lactate causes muscle to stop contraction. Measurement of blood lactate is an easier way to measure what is happening inside the cell. (Just like we measure ferritin to get an indication of bone marrow iron storage for athletes that are anemic.)
As discussed, during intense exercise at anaerobic threshold, a build up of hydrogen ions and attache to hemoglobin, lower muscle ph inhibits enzymes that generate ATP for muscle contraction (12,13,14). If more lactate that is cleared the further use of the oxidative (aerobic) system (15). Lactate is the byproduct of glycolysis which is produced and used by the muscles. The production of lactate is a reaction catalyzed by lactate dehydrogenase which involves the reduction of pyruvate to lactate. The rate of production increases as the exercise intensity increases. The problem with increased lactate production is the association of acidosis.
As the level of exercise intensity increases, the body reaches a point at which the oxygen system can no longer be utilized. At this point, the body begins to produce more lactate. The demands for energy overstress the second phase of the oxygen system and when the systems cannot efficiently and effectively neutralize and metabolize lactate beyond it’s production, acidosis sets in. An emergency system is then activated whereas only carbohydrates are used as fuel. Within seconds or minutes, depending on the athlete’s level of training, exercise performance is drastically reduced (17).
A high lactate value is evidence that the aerobic energy system is failing causing acidosis in and around the cells. Enzymes in the muscle cell may become damaged, which decrease aerobic endurance capacity. Cell wall damage causes leakage from the muscle cell into the blood. A high intensity workout without sufficient recovery causes acidosis which in turn may then lead to injury and overtraining (8).
Lactate threshold, which is also termed anaerobic capacity is expressed as a percentage of VO2 max, is one of the best determinants of an athlete’s pace in endurance events such as distance running and cycling. It has also been thought to reflect the interaction of aerobic and anaerobic energy systems. Researchers have said that this may represent the shift toward anaerobic glycolysis (18).
As exercise intensity approaches 60% of VO2 max, lactate production also increases and correlates with muscle lactate. The intensity at the lactate threshold represents the maximal intensity at which steady state exercise can be maintained (10,18). Every individual can maintain a certain running pace for a long period of time without lactate accumulation. If the pace is increased to a level where acidosis occurs, this forces the person to stop or slow down.
Other explanations for the lactate threshold include a decreased removal of lactate from circulation, an increased recruitment of fast-twitch glycolytic motor units, an imbalance between the rate of glycolysis and mitochondrial respiration, a decreased redox potential, muscle hypoxia (a lower muscle oxygen content), and ischemia (lower blood flow to skeletal muscle) (12).
I know you don’t believe in VO2max concept because we have disagreed on that topic but this is just as an example.
Change in maximal oxygen consumption is used to indicate a change in exercise endurance. Blood lactate response to training adapts to a greater degree than VO2 max. This is especially true with highly trained individuals who may show little or no change in VO2 max, but a change in endurance performance (4).
Coyle et al. (3) compared six ischemic heart disease patients to healthy runners with similar training programs. The patients hade a significantly (P < 0.05) lower
VO2max. Despite having a lower cardiac output the trained patient were able to keep the same speed as the normal subjects. The ability to maintain the same pace was associated with high lactate threshold relative to VO2max. Much research has shown that blood lactate related thresholds can increase with training beyond the point where VO2 max fails to increase (5,6,7,10,11,17).
How can you deny the benefits of using lactate as an aid to exercise performance?
When research has proven that it may help.
Balance,
Ok, I gotcha that sentence that you wrote just through me off.
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