The expression "lactic acid" is commonly used by athletes to describe the intense pain felt during exhaustive exercise, especially in events like the 400 metres and 800 metres. When energy is required to perform an exercise, it is supplied by Adenosine Triphosphate's breakdown (ATP). The body has a limited store of about 85grms of ATP and would use it up very quickly if we did not have ways of resynthesising it.. Three systems produce energy to resynthesise ATP: ATP-PC, lactic acid and aerobic.
The lactic acid system can release energy to resynthesize ATP without oxygen involvement and is called anaerobic glycolysis. Glycolysis (the breakdown of carbohydrates) results in pyruvic acid and hydrogen ions (H+). The pyruvic acid molecules undergo oxidation in the mitochondrion, and the Krebs cycle begins. A build-up of H+ will make the muscle cells acidic and interfere with their operation so carrier molecules, called nicotinamide adenine dinucleotide (NAD+), remove the H+. The NAD+ is reduced to NADH that deposits the H+ at the electron transport gate (ETC) in the mitochondria to be combined with oxygen to form water (H2O).
If there is insufficient oxygen, then NADH cannot release the H+, building up in the cell. To prevent the rise in acidity pyruvic acid accepts H+ forming the lactic acid that dissociates into lactate and H+. Some of the lactate diffuses into the bloodstream and takes some H+ to reduce the H+ concentration in the muscle cell. The muscle cell's normal pH is 7.1, but if the build-up of H+ continues and pH is reduced to around 6.5 then muscle contraction may be impaired, and the low pH will stimulate the free nerve endings in the muscle resulting in the perception of pain (the burn). This point is often measured as the lactic threshold or anaerobic threshold (AT) or onset of blood lactate accumulation (OBLA).
The process of lactic acid removal takes approximately one hour, but this can be accelerated by undertaking an appropriate cool-down that ensures a rapid and continuous supply of oxygen to the muscles.
Astrand et al. (1986) found that the usual amount of lactic acid circulating in the blood is about 1 to 2 millimoles/litre of blood. The onset of blood lactate accumulation (OBLA) occurs between 2 and 4 millimoles/litre of blood. In non-athletes, this point is about 50% to 60% VO2 max and in trained athletes, around 70% to 80% VO2 max.
Lactic acid - friend or foe?
Lactic acid (lactate) is not:
Lactate, produced by the body all day long, is resynthesized by the liver (Cori Cycle) to form glucose that provides you with more energy.
Some of the lactate we produce is released into the bloodstream and used directly as fuel by the heart muscle and liver to make blood glucose and glycogen (Cori Cycle).
The lactate shuttle involves the following series of events:
It has been estimated that about 50% of the lactate produced during intense exercise is used by muscles to form glycogen which acts as a metabolic fuel to sustain exercise.
The Krebs cycle is a series of reactions that occur in the mitochondria and results in ATP formation. The pyruvic acid molecules from glycolysis undergo oxidation in the mitochondrion to produce acetyl coenzyme A, and then the Krebs cycle begins.
Three significant events occur during the Krebs cycle. One guanosine triphosphate (GTP) is produced which donates a phosphate group to ADP to form one ATP; three molecules of Nicotinamide adenine dinucleotide (NAD) and one molecule of flavin adenine dinucleotide (FAD) are reduced. Although one molecule of GTP leads to the production of one ATP, the reduced NAD and FAD production are far more significant in the cell's energy-generating process because they donate their electrons to an electron transport system that generates large amounts ATP.
The Cori cycle refers to the metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles moves via the bloodstream to the liver, converted to blood glucose and glycogen.
The breakdown of glucose or glycogen produces lactate and hydrogen ions (H+) - for each lactate molecule, one hydrogen ion is formed. The presence of hydrogen ions, not lactate, makes the muscle acidic that will eventually halt muscle function. As hydrogen ion concentrations increase the blood and muscle become acidic. This acidic environment will slow down enzyme activity, and ultimately the breakdown of glucose itself. Acidic muscles will aggravate associated nerve endings causing pain and increase irritation of the central nervous system. The athlete may become disorientated and feel nauseous.
Given that high levels of lactate/hydrogen ions will be detrimental to performance, one of the key reasons for endurance training is to enable the body to perform at a higher pace with a minimal amount of lactate. This can be done by long steady runs, which will develop the aerobic capacity using capillarisation (formation of more small blood vessels, thus enhancing oxygen transport to the muscles) and creating greater efficiency in the heart and lungs. If the aerobic capacity is greater, there will be more oxygen available to the working muscles, which should delay the onset of lactic acid at a given work intensity.
Lactic acid starts to accumulate in the muscles once you start operating above your anaerobic threshold. This usually is somewhere between 80% and 90% of your maximum heart rate (HRmax) in trained athletes.
What a low Lactate Threshold means
If your lactate threshold (LT) is reached at low exercise intensity, it often means that the "oxidative energy systems" in your muscles are not working very well. If they perform at a high level, they will use oxygen to break lactate down to carbon dioxide and water, preventing lactate from pouring into the blood. If your LT is low, it may mean that:
Improving your Lactate Threshold
The aim is to saturate the muscles in lactic acid to educate the body's buffering mechanism (alkaline) to deal with it more effectively. The accumulation of lactate in working skeletal muscles is associated with this system's fatigue after 50 to 60 seconds of maximal effort. Sessions should comprise one to five repetitions (depends on the athlete's ability) near full recovery.
Training continuously at about 85 to 90% of your maximum heart rate for 20 to 25 minutes will improve your Lactate Threshold (LT).
A session should be conducted once a week and commence eight weeks before a major competition. This will help the muscle cells retain their alkaline buffering ability. Improving your LT will also improve your tlimvVO2 max.
Lactate Tolerance Training Sessions
The following table identifies some possible training sessions that can be used to improve your lactate tolerance:
Energy production via anaerobic glycolysis, which is particularly essential for events lasting between 30 seconds and 15 minutes, increases the muscle cells' acidity. Soon after, it does the same to the blood. It is this increase in acidity, within the muscle cells, that is a significant factor in producing fatigue. If there was some way to reduce the acidity within the muscle cells, one could theoretically delay fatigue and continue exercising at a very high-intensity for longer.
Sodium bicarbonate is an alkalising agent and therefore reduces the acidity of the blood (known as a buffering action). By buffering acidity in the blood, bicarbonate may draw more of the acid produced within the muscle cells out into the blood and thus reduce the level of acidity within the muscle cells themselves. This could delay the onset of fatigue.
Who might benefit?
The specific athletes who might benefit from bicarb supplementation will typically compete in events that last between one and seven minutes, i.e. 400 metres to 1500 metres running, 100 metres to 400 metres swimming and most rowing competitions.
Van Montfoort et al. (2004) researched 15 competitive male endurance athletes who performed a run to exhaustion 90 minutes after ingestion of a sodium agent. The mean run times to exhaustion were as follows:
The results suggest that sodium bicarbonate supplementation may be beneficial.
A practical approach
Before using bicarbonate, check with your sport's governing body that the substance is not contrary to doping regulations.
It is essential to experiment with the supplement during training and Williams (1996) suggests the following procedure, repeated several times, to determine if bicarbonate supplementation is appropriate for you:
The bicarbonate supplementation protocol would be to ingest 0.3grms of sodium bicarbonate per kg body weight approximately one to two hours before the time trial. e.g. for a 66kg runner, consume 20grms of sodium bicarbonate (about four teaspoons).
The side effects may take the form of pain, cramping, diarrhoea or a feeling of being bloated. Drinking up to a litre of water with the supplementation is often useful, and should be carried out as standard. Breaking up the bicarbonate dose into four equal portions and taken over an hour may also help.
There are potential side effects of taking higher than normal levels of Sodium Bicarbonate, so consult with your doctor first.
Does massage help remove lactic acid?
The subjects were trained runners who performed a maximal treadmill run to elevate blood lactate level and induce exhaustion after 4-6 minutes. Researchers sampled the subjects' blood lactate for up to 20 minutes after exercise. They found that passive recovery (lying down supine) and massage did not affect on blood lactate levels, while mild bicycle riding caused a better removal of blood lactate 15-20 minutes after exhaustive exercise.
This does not suggest that massage is of no benefit to athletes; all it means is that massage does not help remove lactic acid.
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