The expression "lactic acid" is used most commonly 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 exercise it is supplied from the breakdown of Adenosine Triphosphate (ATP). The body has a limited store of about 85 grms of ATP and would use it up very quickly if we did not have ways of resynthesising it. There are three systems that produce energy to resynthesise ATP: ATP-PC, lactic acid and aerobic.
The lactic acid system is capable of releasing energy to resynthesise ATP without the involvement of oxygen and is called anaerobic glycolysis. Glycolysis (breakdown of carbohydrates) results in the formation of pyruvic acid and hydrogens ions (H+). 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 which deposit the H+ at the electron transport gate (ETC) in the mitrochondria to be combined with oxygen to form water (H2O).
If there is insufficient oxygen then NADH cannot release the H+ and they build up in the cell. To prevent the rise in acidity pyruvic acid accepts H+ forming lactic acid which then dissociates into lactate and H+. Some of the lactate diffuses into the blood stream and takes some H+ with it as a way of reducing the H+ concentration in the muscle cell. The normal pH of the muscle cell 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 or onset of blood lactate accumulation (OBLA).
The process of lactic acid removal takes approx. one hour, but this can be accelerated by undertaking an appropriate warm down which ensures a rapid and continuous supply of oxygen to the muscles.
The normal 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:
- responsible for the burn in the leg muscles when exercising very fast
- responsible for the soreness you experience in the 48 hours following a hard session
- a waste product
Lactate, which is produced by the body all day long, is resynthesized by the liver (Cori Cycle) to form glucose which provides you with more energy. Sounds like a friend to me.
The lactate shuttle involves the following series of events:
- As we exercise pyruvate is formed
- When insufficient oxygen is available to breakdown the pyruvate then lactate is produced
- Lactate enters the surrounding muscle cells, tissue and blood
- The muscle cells and tissues receiving the lactate either breakdown the lactate to fuel (ATP) for immediate use or use it in the creation of glycogen
- The glycogen then remains in the cells until energy is required
65% of lactic acid is converted to carbon dioxide and water, 20% into glycogen, 10% into protein and 5% into glucose.
The breakdown of glucose or glycogen produces lactate and hydrogen ions - for each lactate molecule, one hydrogen ion is formed. The presence of hydrogen ions, not lactate, makes the muscle acidic which 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 greater pace with a minimal amount of lactate. This can be done by long steady runs, which will develop the aerobic capacity by means of capillarisation (formation of more small blood vessels, thus enhancing oxygen transport to the muscles) and by creating greater efficiency in the heart and lungs. If the aerobic capacity is greater, it means there will be more oxygen available to the working muscles and this 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 is normally somewhere between 80% and 90% of your maximum heart rate (MHR) in trained athletes.
What a low Lactate Threshold means
If your lactate threshold (LT) is reached at a low exercise intensity, it often means that the "oxidative energy systems" in your muscles are not working very well. If they were performing at a high level they would 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:
- you are not getting enough oxygen inside your muscle cells
- you do not have adequate concentrations of the enzymes necessary to oxidize pyruvate at high rates
- you do not have enough mitochondria in your muscle cells
- your muscles, heart, and other tissues are not very good at extracting lactate from the blood
Improving your Lactate Threshold
The aim is to saturate the muscles in lactic acid which will educate the body's buffering mechanism (alkaline) to deal with it more effectively. The accumulation of lactate in working skeletal muscles is associated with fatigue of this system after 50 to 60 seconds of maximal effort. Sessions should comprise of one to five reps (depends on the athlete's ability) with near to full recovery.
Training continuously at about 85 to 90% of your maximum heart rate for 20 to 25 minutes will improve your 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 tlimvVO2max.
Lactate Tolerance Training Sessions
The following table identifies some possible training sessions that can be used to improve your lactate tolerance:
||3 x 3|
||2 x 4|
Energy production via anaerobic glycolysis, which is particularly important for events lasting between 30 seconds and 15 minutes, increases the acidity inside the muscle cells, and very soon after does the same to the blood. It is this increase in acidity within the muscle cells that is a major factor in producing fatigue in such events. If there was some way to reduce the acidity within the muscle cells, one could theoretically delay fatigue and thus 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 be able to 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.
Research indicates that sodium bicarbonate ingestion can improve your lactate threshold. Richard Kreider (University of Memphis) conducted a six day trial with a Sodium bicarbonate supplement where 4 grams/day were consumed. At the end of this period VO2max was improved by 9%, LT raised by 12% and blood-haemoglobin levels by 5%.
Who might benefit?
The specific athletes who might stand to 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, most rowing competitions, and many team sports with their repeated nature of high intensity exercise which stresses the anaerobic glycolysis system significantly and produces a lot of acidity.
A practical approach
Before using either bicarbonate, it is wise to cheek with the governing body of your sport that the substance is not contrary to doping regulations. The most important practical point is the need to experiment with the supplement during training. Typically, an 800 metre runner, may perform a time trial on a particular day after a couple of days of light training. A further couple of days later, after only more light training, he/she can repeat the time trial in a similar environment after bicarbonate supplementation. The exact protocol would be to ingest 0.3 grms of sodium bicarbonate per kg body weight approximately one to two hours before the time trial. That is, for a 66kg runner, consume 20 grms of sodium bicarbonate (about four teaspoons) and, yes, the commonly found bicarb of soda is exactly the substance needed. This experimenting, if repeated several times, should reveal whether bicarb supplementation is likely to produce any benefit and whether the athlete concerned is susceptible to any side effects.
It is likely that large individual differences do exist as far as response to supplementation is concerned. It has been suggested that the more highly trained athletes are less likely to benefit from it because their body's natural buffering systems are already so well developed, but so far this is just speculation. It has also been shown that sprinters build up more acidity within their muscles than endurance runners in response to the same exercise, and so may be more likely to benefit from the buffering effect. From the scientific research, it appears that the size of the dose is quite important, and that taking only 0.2 grms per kg is less likely to be beneficial than 0.3 grms per kg, although no evidence exists suggesting that an even greater dose is better still.
As for the side-effects, these may take the form of pain, cramping, diarrhoea or a feeling of being bloated, the athlete who suffers must try to eliminate them. Drinking up to a litre of water with the dose is often effective and should be carried out as standard. Breaking up the bicarbonate dose into, say, four equal portions taken over the course of an hour may also help.
There are potential side effects to taking higher than normal levels of Sodium Bicarbonate so consult with your doctor first.