Lactate - what is it?
Joe Dunbar provides an overview of the body's energy systems and the foe of all endurance athletes - Lactic Acid.
The term lactic acid, or lactate, is used by some in the field of research in sports science, while others may use the term in describing that pain felt in the body during exhaustive exercise, but what is it? It is usually feared by most athletes, as the term lactate is commonly associated with that intense pain felt in the legs and arms at the end of a race or hard session, especially in short events like the 400m or 800m. However, lactate is not all bad because it can act as a useful marker that may help in the planning of effective training programs.
In describing lactate, it is vital to have a brief understanding of energy systems, the mechanisms the body uses to supply energy to the working muscles. This does not mean that we have to plunge deeply into the realms of biochemistry and physiology, but a few fundamental principles have to be established.
For the muscles to contract, they need energy and molecules of ATP can supply this. This ATP, however, must be provided to the muscle when exercise continues as the amount stored in a muscle at any one time is enough for only a very short period. There are indeed three methods the body can use to supply energy, in the form of ATP, to the working muscles. Two of these methods, or sources of energy supply, can be considered anaerobic (they do not require oxygen immediately for their chemical processes) and the other is considered aerobic, where a steady supply of oxygen is available to meet the demand of exercise. The anaerobic sources can be split again, into either lactate or alactate. When the muscle's immediate stores of ATP are exhausted (within a fraction of a second), chemical changes to creatine phosphate, also stored in the muscle, can give the muscle extra ATP. This is considered an alactate source of ATP because no lactate is produced. Again, this source of ATP is relatively short-lived, so the body has to utilise another method to continue to supply a working muscle with these units of energy.
Glycolysis is the term used to describe the energy pathway that is used in producing molecules of ATP from a molecule of glucose. A series of biochemical reactions take place within the muscle cells after which, if oxygen is present, another series of reactions is embarked upon, and the process is considered aerobic. Provided there is plenty of oxygen and other fuels needed in the chemical reactions, and the exercise maintains at a steady-state, it is possible to sustain aerobic exercise for a long time. However, if there is not enough oxygen present, then lactic acid is produced, an oxygen debt is incurred, and the process is considered anaerobic. This is all very well, after all, if the body can still produce ATP to fuel the muscle without oxygen, there is no problem, is there? Well, it is not quite as simple as that, because if the acid conditions continue, the functioning of the body will become impaired and the muscles will fatigue very quickly. In this respect, lactate can be considered as bad news for the athlete, as it is one of the factors that will lead to fatigue, at least in the shorter, middle distance events.
To put the idea of energy systems into practical terms, it is useful to give an everyday example. If a bag of sugar is sitting on a table, and a person picks it up, the muscles would not need oxygen, as you could still do this activity while holding your breath. The exercise would be anaerobic and alactate. If the person then decided to hold their breath and pick it up and put it down quickly, 40 times, the work would still be anaerobic, but they would probably begin to feel discomfort, as lactate would probably build-up, causing local fatigue. If the bag were then lifted and put down 100 times, at a steady rate, the exercise would probably be aerobic because the body would be able to take in sufficient oxygen to meet the demands of the exercise.
It should be remembered that the energy systems are all working together at the same time. It is just that the amount of energy or ATP derived from each system may vary according to the conditions and intensity of the exercise. For example, during a 10-second sprint, there would be a contribution from all of the energy sources. The ATP in the muscle would be used immediately. Still, at the same time, some ATP would be supplied by anaerobic glycolysis (producing lactic acid as one of the waste products) and some from aerobic sources. It is just that most of the ATP would be supplied anaerobically. If the exercise was of longer duration, the contribution from anaerobic sources would be less but made up by a more significant contribution by the aerobic source.
If an athlete starts a steady five-mile run, it might take a few minutes for the heart rate to increase and the blood supply to be at its optimal level. This might mean that there is not quite enough oxygen to fuel this exercise fully aerobically, and in the short term, the ATP might be supplied more by anaerobic sources. As the athlete warms up, however, his/her body will become better adapted for the exercise and will shift to become exercising in a more aerobic state. In terms of lactate, then, it is possible that at the start of a steady run, there may be an increase in lactic acid in the muscles that will gradually be reduced as aerobic sources slowly meet the demands of the exercise.
If the athlete is performing a run at slightly greater intensity, for example in a five-mile race, after adequate warm-up, there will likely be an element of lactate build up. This is because there is a contribution of anaerobic energy production involved, as well as aerobic energy production. If the athlete produces a finishing kick at the end of this five-mile race, he/she will still be using aerobic source, but will also use his/her anaerobic sources to a greater extent, not only in terms of lactate build-up but also in the alactate department. The key to judging the kick is knowing the furthest point from the finishing line that maximum effort can be thrown in before lactic acid takes over and limits the ability of the muscles to perform is.
In an exercise, the greater the intensity of exercise, the higher the lactate levels are likely to be. So, you would expect to see greater lactate levels at the end of an 800m race than a marathon, because the intensity of exercise would be much greater in the former. Lactate is produced in working muscles, as a waste product. It can be oxidised, either when the exercise is halted or slowed down so that the aerobic capacity of the individual is sufficient to meet the demand of the exercise being performed. As the lactate is produced in the muscles it leaks out into the blood and is carried around the body. This is why measuring blood lactate is a good reflection on how hard the individual is working. There is a very good correlation between muscle lactate (which is much more difficult to try to measure) and blood lactate.
When lactate is produced in some muscles during very hard exercise, it can be taken to other muscles which are not working, or other organs of the body, to be oxidised. It can also shift across to different fibres to be oxidised. It has been found that fast-twitch fibres generally produce more lactate than slow-twitch.
This is most likely to be the reason why at exhaustion, a sprinter will have greater lactate levels than, say, a marathon runner. The muscles of a sprinter are likely to have a much greater ratio of fast-twitch fibres, while the marathon runner will have fibres of predominantly slow-twitch.
Further, speed work is likely to increase the maximum amount of lactate present in the muscles during intense physical exercise, probably because the body learns to recruit more fast-twitch fibres, which may also become better developed.
Given that high levels of lactate will be detrimental to endurance performance, one of the critical reasons for endurance training is to enable the body to run at a greater pace with a small amount of lactate. This can be done by long, steady-state endurance running, which will develop the aerobic capacity, using capitalisation (formation of more small blood vessels, thus enhancing oxygen transport to the working muscles) and by creating greater efficiency in the heart and lungs.
If the aerobic capacity is greater, it means that there should be more oxygen available to the working muscles, and this should delay the onset of lactic acid at a given work intensity.
However, another way of developing aerobic capacity is threshold running and interval work. Here the body works at an intensity that produces a greater amount of lactate. Thus the anaerobic system is challenged as well as the maximum aerobic capacity.
VO2 max is often quoted as a good indicator of an individual's fitness. The VO2 max is a good general indicator of endurance fitness and was, up to the 1970s, the gold standard measurement of aerobic ability. In recent times, however, sports science has progressed, giving a more sensitive measure of an athlete's condition by measuring blood lactate during exercise.
We now understand what lactate is, so now we will look at the advantages of lactate testing while warning of the possible limitations in using such a method as an aid to endurance training. Lactate testing can be a handy tool in prescribing exercise intensities, provided sufficient knowledge is available from the physiologist, along with interaction with the coach and athlete.
One of the advantages of lactate testing is that it may be more sensitive to changes in fitness than the VO2 max test. This has been confirmed in several research studies over the years. Still, one of the most recent was by Faulmann and co-workers at the British Olympic Medical Centre (BOMC), who presented their data in Vancouver in April. Although the athletes studied were biathletes and Nordic skiers, the principles would apply to all sports. The research showed that after five months of endurance training, the VO2 max did not change significantly. Still, the running speed at a set lactate concentration of 2.5mmol/l did increase considerably from 4.66m/s to 5.09m/s.
This should not be too surprising, however, as much contemporary research has shown that the VO2 max of a training individual will increase over time until it eventually reaches a plateau. Lactate testing, therefore, offers another variable to be assessed when monitoring the fitness of high-performance athletes. We know after all that an individual may have a stable VO2 max through a hard training period. Yet, the fitness of that individual may be increased significantly, and this change in fitness is usually reflected in the lactate response to exercise rather than the VO2 max measurement.
A second major advantage of lactate testing over the VO2 max is that the lactate test is submaximal, as opposed to a run to exhaustion seen in the VO2 max test. This is not usually a problem in competitive athletes, who are used to striving in painful conditions to get the best out of themselves. Still, the VO2 max test may not be an accurate indication of fitness in the de-motivated athlete, who may be unwilling to give their all in a run test to exhaustion.
At this stage, you may well be asking, "What exactly does a lactate test involve?" There are no hard and fast rules about how to assess an individual. Still, in this country, the physiology section of the British Association of Sports Sciences (BASS) has issued a series of guidelines, which are currently under review. This should prove to be a useful procedure because since the guidelines were published in the 1980s, science has inevitably progressed, and new ideas have been put forward towards creating better tests to help the athlete and coach.
The testing would be done in laboratory conditions, which would remove the effect of environmental influences. The runner would perform his/ her work on a motor-driven treadmill. Usually, four running speeds would be used, each lasting four minutes in duration. At the end of each running speed, a small blood sample would be taken from the individual and subsequently analysed for the blood lactate content. There is variation in the testing protocols used in the different labs around the world. Some labs, for example, use the BASS guidelines and therefore, the procedure would be to have the four speeds continuous following each other. Other labs tend to split the running speeds up with recovery periods. This may be more useful when using the test results for exercise prescription, as the scientist can be more confident that the workloads will be isolated. That is to say that the lactate level measured in the athlete at a particular running speed is not affected by the previous running speeds that may have been tackled by the athlete.
It is this type of difference that should make athletes, coaches and physiologists very wary when reading research performed in different labs around the world. If recommendations are to be used from various pieces of research, it is vital to make sure that it is understood exactly how the results have been gathered. There are other differences in ways of assessing fitness via lactate analysis.
Some labs feel that four minutes may be too short a time to get a true reflection of the lactate level for a particular running speed. Similar to the way it can take time for the heart rate to rise to a correct level for a set running speed in an athlete running, the lactate could take more than four minutes to stabilise. Sometimes the lactate level will be high initially, but as the athlete settles into the workout, the lactate level may drop to a more stable level, especially if the speed is relatively low for the athlete and he/she can run in a fully aerobic manner. If a running speed is very fast, it is unlikely that the lactate level will ever stabilise. Instead, it will continue to increase with time, usually in an exponential manner until the athlete comes to a halt, due to exhaustion.
Another point to be wary of, when reading the literature on lactate and training, is how the lactate is measured. Unpublished research was done at the BOMC, where hundreds of blood samples are taken from exercising athletes every week, and the laboratory at St Mary's College, Twickenham, have shown that there can be a difference in the lactate level depending on where the sampling site was. For example, blood samples taken from the fingertip often appear to be a fraction higher in lactate concentration than blood taken from the earlobe. This, so far, is only an observation and has not yet been analysed in proper research fashion but does indicate that differences may occur depending on the sampling site. Another difference that can occur is if the blood sample is one of whole blood, or from the blood plasma.
Different labs may use different types of sample, some favouring whole blood, some plasma, but again it is necessary to note what method has been employed when reading the literature. This is indeed critical when reading articles that may recommend training based upon lactate levels. For example, a research paper from Germany might recommend training for 20 minutes at a speed that will elicit a blood lactate concentration of 4mmol/l. Suppose they have established this using plasma lactate, but your athletes were tested using whole blood samples. In that case, the athletes may well be training at a four mmol/l level, but this is not necessarily the intensity recommended. It is perhaps here that the skill of interpretation is of utmost importance to the setting of training intensities.
A different problem of lactate testing in terms of interpretation was pointed out by Busse, Maassen and Braumann (Leichtathletik vol 38, no 38 1987). They were perplexed at the scepticism of athletes and coaches when it came to lactate testing. The reason they were sceptical was that the training intensities set by the physiologist were not always possible for the athlete to maintain. Busse and co-workers pointed out that the reason for this was most likely to be a result of the athletes having low stores of muscle glycogen before the lactate test.
If this is the case, the athlete will not be able to produce lactate, and this may indeed give a false picture of the condition of the athlete, in that the athlete would have artificially low lactate levels at relatively tough running speeds. This emphasises the importance of being well-rested for physiological assessment in tandem with making sure that the athlete has eaten sufficiently well in the days before and during the test, to ensure the muscle glycogen stores are replenished. An athlete should prepare for a test as he/she would for a hard training session or small competition.
To monitor an athlete's condition using lactate analysis is straightforward. The most common method is to plot the lactate data against running speed, on a graph. The lactate data on the graph will characteristically form a curve upwards with the increase in running speed. Therefore, at first, the rise in lactate with running speed is relatively small, but beyond a certain point, this increase will become far more vigorous. It is this point that is commonly referred to as the lactate threshold or anaerobic threshold. Extensive research has shown that training at a level just below this point is a useful way to improve the athlete's aerobic capacity. Many terms exist for this type of training, but one of the most common is threshold training. Training at this threshold level can be done in the form of a continuous run of say 20 to 30 minutes duration or can be split into repetitions, for example, mile reps.
The intensity could be set via the speed, but problems may exist here, because the terrain may vary, or the athlete could be training in windy conditions. The way around this problem is to measure heart rate simultaneously during the lactate test. It can then be established what heart rate will elicit a specific desired lactate level. If the athlete then uses a heart rate monitor while training, there can be a reasonable level of confidence that that athlete is training at the appropriate training intensity. In threshold running, the key aspect is to get the speed just right so that the athlete is running as quickly as possible without going over the 'threshold' level, as this will result in rapid acidosis and fatigue. This is one of the key points that comes across in the book by Janssen ('Training Lactate/ Pulse Rate'. Polar Electro Publishers, Oulus, Finland 1989). On the other hand, if the athlete is not going quite quickly enough, then the maximum benefit of the workout will not be enjoyed.
The heart rate monitor can be a handy tool in the avoidance of overtraining, a major fault of many motivated athletes. If athletes are performing interval sessions a couple of times per week, their steady runs should be of a nature that there is no great production of lactate. The athlete should, therefore, train within sensible limits so that they are in a state to perform the next high-quality interval session to good effect and not hindered by overdoing it on the steady runs. Wearing a heart rate monitor with an alarm can prevent the athlete from overtraining, provided that the correct limits are set on the watch. These limits can be set via the lactate test, so the athlete and coach will have a good idea of the lactate levels of the athlete while training because the heart rate will reflect the lactate data.
To enhance the confidence of the athlete, a field test can be performed. This would mean that the athlete would perform a normal training session, whether it is an hour run for base endurance, or 5x800m, with the heart rate monitor on. If lactate samples are taken at fixed intervals through the session and analysed by a portable lactate analyser (which are becoming increasingly available on the market at competitive prices), a check is made possible. Therefore, the athlete, coach and physiologist can check that the lactate level that is aimed at with the use of the heart rate (established from the lab-based lactate test) is indeed the lactate level that is experienced by the athlete while training outdoors.
Each individual is different, so rather than every athlete training at set lactate levels (2 and 4mmol/l levels have often been used in the past) the physiologist should advise the athlete as to what levels they should be training at. Different individuals will produce higher or lower amounts of lactate, depending upon factors, such as muscle fibre composition. The individual should be treated as an individual, and so a lactate profile for that athlete should be recorded, and the training prescription evolved from such an individual profile.
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