Lactate Testing - Questions
We find there are many misconceptions about lactate among both athletes and coaches. This page is an attempt to clarify what is known about lactate, lactate metabolism, lactate testing and its appropriate use in the training of athletes. Within this entire web site there is probably the most detailed discussion of lactate on the internet. The discussion is even more extensive on the Secrets of Lactate CD-ROM.
Questions posted May 4, 2012.
- What is Lactate?
- Lactate is an organic molecule. In past versions of this page we have said it was a carbohydrate. It is technically not a carbohydrate, but an ion with a negative charge, or an anion. Its chemical formula is C3H5O3-. It is found in every cell in the body; it is on the skin and in sweat and saliva. It is harmless.
- What is Lactic Acid?
- Lactic acid is an organic molecule. Its chemical formula is C3H6O3 Lactic acid has the same proportion of carbon, hydrogen and oxygen as carbohydrates but it is technically not a carbohydrate. It is rarely found in the body. It is harmless. Many people believe wrongly that lactic acid occurs in the muscles after hard exercise, causing a burning sensation. This is not true. Actually, if lactic acid is produced in the body, it breaks down almost immediately into lactate and hydrogen ions. What persists in the body is lactate. Notice the chemical formulas are very similar. A very kindly and professional chemist suggested some of the wording in these definitions.
- Does lactate or lactic acid have anything to do with breast milk or lactation? What about lactose intolerance?
- No. Lactic acid was discovered in sour milk in the late 1700's. Because it was discovered in milk, it was given the name lactic acid. But that is it. There is no connection to lactation or lactose intolerance or a type of milk called Lactaid.
- Why is Lactate physiologically important for an athlete?
- During training and during a competition, the body needs fuel for the energy that is required for the muscles to contract fast enough for the specific event. The two main energy systems are the aerobic and anaerobic systems*. Lactate is the output of the anaerobic system; after that it performs its most important function. It is the main fuel for the aerobic system during competition and much of training. A very persistent myth is that lactate is a waste product. Nothing could be further from the truth. It is amazing how some erroneous ideas are hard to kill. It is actually a major fuel source for the heart and the brain as well as skeletal muscles.
Measuring lactate is a way of assessing how strong each system is, or how well-conditioned the athlete is at a specific point in time. No other measure provides this information. Thus, measuring lactate with an appropriate test is the best way to measure the conditioning level of an athlete during training and prior to a competitive event.
Because of this, using the right types of lactate tests periodically is the best way to know if the training of an athlete is working and will lead to an optimal performance.
*There are actually two anaerobic systems but only one plays a role in most athletic events. A much more detailed discussion of anaerobic energy production and lactate is on our triathlon site.
Questions posted May 5, 2012.
Theoretically the best place to measure lactate to see what is happening during exercise and competition is in the muscles themselves. But this is impossible without doing muscle biopsies. That is why most measures of lactate take place in blood. If measured properly, lactate levels in blood will reflect pretty accurately what is happening in the muscles. But because it takes time for the lactate to leave the muscles and get to the bloodstream, the protocol for measuring lactate must be appropriately timed.
During training or a race, if the athlete is moving at a constant effort, the lactate produced in the muscles will flow to various places in the body including the bloodstream. The levels of lactate in the muscles, interstitial fluids and the bloodstream will come to equilibrium. So measuring the lactate in the blood is a very good indication of the level of lactate being produced in the contracting muscles. If the athlete increases or decreases the effort level the amount of lactate produced in the muscles will change. Depending upon the amount of the change, the time it takes for the lactate levels to come to a new equilibrium will vary. If the athlete increases the effort level substantially then it will take longer for the lactate levels to level out.
But we will see that there is an effort level past which there is no equilibrium — lactate levels in the muscles will continually increase. Because of this lactate levels in the bloodstream also continually increase. This effort level is very important for race performance. The metabolism within some contracting muscles has changed dramatically; this will affect how fast the athlete can compete. We will call this effort level, "the lactate threshold." But before anyone objects to our definition for this term, we recognize that many others will not use the term "the lactate threshold." as we do. This will be discussed in detail in subsequent questions.
A lactate analyzer will measure the lactate in a blood drop. Researchers have tried to use saliva and sweat to measure lactate, but the levels and response time are not predictable. Hence nearly every lactate test is done using a blood drop. Years ago this was done only by researchers or technicians in a laboratory setting but today portable lactate analyzers are relatively inexpensive, very accurate and widely available. For most athletes there is no economical reason not to measure lactate.
So if someone says that is it difficult to measure lactate, they are apparently not aware of how easy it is today. An athlete may decide that they do not want to measure lactate because of cost, or they think they can get the same information in other ways or they do not know what to do with the results or for a variety of other reasons. This site hopefully, will show the average coach and informed athlete just how to use the lactate test results and that there is no other convenient source with similar information.
Questions posted May 6, 2012.
We then had him sit on a bicycle trainer and asked him to pedal at 100 watts for about 5 minutes. We then took his lactate reading again and it was almost the same as the reading when he was sitting in a chair. Again he asked what it meant and we told him that we had to increase the power to show him differences. In order to shorten the process, we asked him to pedal at 200 watts for five minutes. This is not a good way to do a proper lactate test but it shortened the process since we were interested in quickly showing him why lactate was a valuable measure.
It was still relatively easy for him but he was breathing a little bit harder. His lactate reading went up about 50%. We then asked him to pedal at 300 watts for 5 minutes. He couldn't finish the 5 minutes and the lactate reading was about 4 times the level at 100 watts. After a couple minutes we took another lactate reading and it was now even higher, about a third higher than it was just three minutes before and the athlete had been sitting all the time in a chair.
We then explained to him that lactate readings are mainly useful only in an exercise environment. Taking a lactate reading while sitting told us nearly nothing about his conditioning but taking a lactate reading after exercising at a specific exercise intensity told us a lot more. Certainly it did not tell us everything since the test we did was very imprecise and meant only to show the athlete how lactate varies depending upon the situation.
The lactate results are almost the same for this step at 210 watts and the next one at 240 watts. At 270 watts the curve rises a little. At each subsequent step the lactate levels are higher, and at 390 watts the athlete could not continue. Notice that the lactate results change very little at low levels and then suddenly shoot up. At the same time heart rate increases in a straight line. So what does all this mean? Further questions will address this as we try to understand just what is happening in the athlete's muscles.
**There are times when a resting lactate can tell you a lot, especially if the person has additional resting lactate readings from other times. A subject for a future question.
Questions posted May 14, 2012.
The lactate curve has been described as an exponential curve (not actually the case as will be discussed later) and the heart rate behaves essentially in a linear fashion. Let's look at a different combination of factors: lactate and oxygen consumption. The chart below is one of several we have for college soccer players. It compares oxygen consumption with lactate, while the subjects are running on a treadmill. The oxygen curve is essentially a straight line like the heart rate, while the lactate curve shows a curvilinear pattern. A resting lactate taken just before the exercise is indicated on the left hand side of the chart. The lactate levels were taken with the Lactate Scout.
One interesting thing about this curve is that the first couple of lactate readings are lower than the resting lactate value. This is not unusual and can be explained by the interactions of the different energy systems in the muscle cell and how lactate is actually consumed by the muscles. We will discuss in a later question just why in some circumstances lactate readings at easy exercise levels can be lower than resting lactates.
Again notice how the oxygen consumption increases in a linear fashion. Oxygen consumption increases from about 53% of VO2 max to about 80% of VO2 max and the lactate levels are only a little above the resting lactate levels. Then lactate climbs rapidly. So heart rate and oxygen consumption are linear and lactate is not. The lactate curve changes quickly as intensity gets higher and oxygen consumption becomes much higher.
Why? Does it mean that the lactate is not being produced at low effort levels and is suddenly switched on at some point in large amounts? That is what a lot of scientists thought years ago but it turned out not to be true. Lactate is being produced as one sits and reads this web page and it has nothing to do with a lack of oxygen. Then why does it behave in the fashion we see on these charts.
The answer is twofold.
- First, lactate is the output of the anaerobic system and the main fuel of the aerobic system during exercise. So if lactate is being produced at low levels, it will never get to the bloodstream where it can be measured because it will be consumed by the aerobic system. The following figure is a simplified diagram of the energy metabolism process.
Diagram of basic aerobic and anaerobic energy producing processes
Notice two things.
- (1) it is not lactate but pyruvate that is the output of the anaerobic system. But pyruvate is an intermediate step, which turns almost immediately into lactate.
- (2) lactate can enter the bloodstream or turn back into pyruvate. If lactate turns back into pyruvate, it will enter the aerobic system and be used as a fuel. There will be no change in the lactate levels in the bloodstream. So lactate is produced continually, but at low effort levels, most is immediately consumed by the muscles. The output of the aerobic system is energy, water and carbon dioxide; no change in blood lactate levels are noticed. Thus, at low levels a lot of the lactate produced never enters the blood stream. At higher exercise levels not all the lactate produced by the anaerobic system can be consumed by the originating muscles. Some will spill out into the bloodstream and the lactate levels in the bloodstream will rise.
In a later question we will discuss where the lactate comes from that is in a resting subject.
- Second, lactate is the output of the anaerobic system. The output of the anaerobic system relative to the aerobic system is very low at low effort levels. As intensity increases, the anaerobic system gradually provides a higher percentage of energy. Thus, at low intensities very little lactate is produced but it increases very rapidly with exercise intensity. Here is a sample curve of lactate production in the muscles during exercise.
If you are familiar with lactate curves, this curve has a familiar shape. However, it differs from typical lactate curves in that it plots the rate of lactate production against VO2. It also shows the rate of lactate production in the muscles rather than in the bloodstream. This curve is based on a model of energy production developed by Alois Mader, one of the most prominent scientists to study the relationship of lactate to athletic performance. Mader was originally part of the East German sports science establishment but escaped to West Germany in the early 1970's. He investigated the changes in the muscles as exercise intensity increased and found out the key factor was how the two energy systems interacted. Most researchers thought that the reason the anaerobic system rose in its contribution to the total energy needs of the athlete as energy requirements got higher was due to a lack of oxygen. Mader discovered a very different relationship that was due mainly to the relative strengths of each system. He found that the anaerobic system's involvement in producing energy was affected by the strength of the anaerobic system compared to the strength of the aerobic system. In other words the relative strength of the two systems is what determines how much of each is utilized, not the presence or absence of oxygen .
It turns out that the rate of production of lactate is due to interactions between the two energy systems. The stronger one system is, the less the other is utilized during exercise. Or the converse is also true, the weaker one system is, the more the other will be utilized.
Questions posted July 5, 2012.
During normal everyday activities, blood lactate levels vary, but not by much from one hour to the next. With strenuous exercise they go up; and if we lay in bed for an hour they might go down a little. Essentially the lactate level at any time would represent the result of normal biological processes that produce and eliminate lactate. At rest or low activity, lactate is mainly produced by the red blood cells and eliminated by aerobic processes as well as by the liver. A typical lactate level over the course of a 16-hour day without any strenuous activity would look like the following chart:
It fluctuates a little, but at rest the production of lactate Lp is much less than the processes that eliminate lactate Le. The average for this particular day is 1.44 mmol/l. During normal daily activity there is constant production and constant elimination. The difference between one time of the day and another is not totally understood, but some variance is due to food intake, which seems to affect lactate production. (The red blood cells are the only cells in the body that do not have mitochondria and thus all their energy is generated by anaerobic processes which produce lactate as an end result).
Most of the lactate is being eliminated or removed by the aerobic process in cells all over the body with some of the lactate being converted back into glucose in the liver. When one begins exercise, more lactate is produced than at rest so Lp increases. But the clearance processes Le continue to eliminate lactate from the system. So it sometimes looks like there is no change in blood lactate even though the body is producing more. Here are typical lactate values over a 30-minute period for different levels of exercise.
For the chart above Lp is increasing as the intensity of the exercise gets harder. Each line represents a slightly harder effort (from blue to red to green to purple to teal to brown). But for the first five effort levels, the elimination capability Le is equal to or higher than the production rate Lp. That is why each line represents a steady state. For the sixth level (brown line) Lp is greater than Le and the lactate levels continue to rise – there is no steady state. Eventually athletes have to stop at this effort level because of the increase of various metabolites which causes the muscles to get very acidic.
At rest and at low effort levels the lactate elimination processes are such that the lactate produced is mostly removed locally. Little if any lactate ever enters the bloodstream. If some lactate enters the bloodstream it is being taken out in equal amounts someplace else in the body. So there is little or no increase in observed lactate levels in the bloodstream. In other words the Le elimination rate is much higher than the lactate production rate Lp. In the chart below is a typical graded lactate test. The first part of this curve is flat and is often referred to as the baseline. Lp is increasing but not enough to affect the blood lactate levels. If one could actually measure lactate in the muscles, the results would show small increasing levels of lactate even though the levels in the blood have not risen.
From 180-240 watts there is little or no change in blood lactate levels which are similar to resting levels for this particular athlete. At these effort levels Le is still much greater than Lp and the body gets rid of all the new lactate being produced.
At 270 and 300 watts Lp is even higher but still Le can keep it at a steady state but now the lactate level is higher than the baseline. Lp has increased significantly and causes the lactate in the blood to rise but Le can still remove an equivalent amount. The exercise is still steady state but blood lactate is now higher. Eventually the elimination rate cannot keep up with production and lactate levels rise rapidly in the blood.
The following chart is based on a simulation program that predicts several metabolic variables. In this chart muscle lactate is shown by the green line, while the blood lactate line is yellow. Notice how blood lactate lags lactate levels in the muscles. Muscle lactate indicates how much lactate is being produced Lp but even while still in the muscle, some of the lactate is used immediately as a fuel. The blood lactate is a net of production Lp minus elimination Le, much of which happens in other places in the body.
The next chart shows what would happen to lactate in the blood if the athlete changed the effort level every 6 minutes. The athlete would change from one steady state to a higher one every 6 minutes but eventually reach a point above any steady state.
We have simplified the process by pointing out that a lactate value is just the result of two natural processes, lactate production Lp and lactate elimination Le. Now let's look at two lactate tests taken with the same athlete at two different time periods.
The early and late season tests are very similar at the first five low effort levels. But the next three readings show substantial divergence. We know from above that the lactate value is the net result of the elimination Le and production Lp processes. So which is it? Or could both have changed? We know that at least one of the two processes has changed. If this is an endurance athlete, it is a change that will let the athlete compete at a faster pace most of the time. But why do the muscles produce less lactate or eliminate more, later in the season? The answer to this is the secret of training and the main reason an athlete spends so much time working out.
Before we go on to another question, let's look at the diagram above on energy metabolism but this time note the lactate production Lp and lactate elimination Le.
This illustrates that lactate production and lactate elimination are essential parts of energy metabolism and shows why the measurement of lactate is so important. Lactate values demonstrate how well the two energy systems are developed. This will be the greatest determinant of race performance. So lactate is the key to understanding how well the athlete is conditioned for a particular event.
Why for a particular event? The reason is that at a particular moment an athlete may be optimally conditioned for one event but not another. For example, two runners with equal VO2 max's may not be able to perform equally well in the same event. One may excel in a marathon while the other would beat this runner handily at 1500 m. Lactate metabolism is key to understanding just why this is so.
***Steady state exercise are those intensities that are below the maximal lactate steady state. Lactate levels, heart rates, VO2 consumption and perceived effort change only small amounts over a time period, usually at least 50 minutes and sometimes much longer.
This page will be updated with additional questions and our attempts to answer them. Submit a better answer if you think you can improve on what we have here or if you think you have found a mistake. We want the page to accurately reflect what we believe is correct.Also send any questions you might have about lactate testing and lactate analyzers and we will try over time to post answers. Some questions we may not be able to answer.