Most serious rowers have heard of lactic acid. Usually, they know little more about it than it is the stuff that makes their muscles cramp after they have worked to exhaustion.
This article intends to explain what lactic acid is and why it is important in athletic training. It will also tell you how you can measure your own lactic acid levels and how that information can improve your rowing performance.
What is Lactic Acid and How is it Related to Exercise? Every time a muscle contracts, it makes some lactic acid. Usually, this doesn't matter. Moderate amounts of lactic acid are burned for energy in resting muscle. At higher levels, lactic acid can be dumped out of muscle into the blood. But sometimes, muscle exertion makes huge amounts of lactic acid and the muscle has trouble getting rid of it. This can have deleterious effects. It all depends on how long and how hard the muscle has been working.
Whenever a muscle contracts, it takes energy from a compound called ATP and makes a product called ADP. Muscle uses a host of mechanisms to regenerate ATP from ADP so that it can keep on working. All of the regeneration mechanisms can work at the same time, but at different levels of exertion, different mechanisms tend to be the major ATP supplier.
Starting from rest, the initial demand for contraction energy is met by a fuel reserve called creatine phosphate. This energy source is unique to muscle. It required no oxygen and makes no lactic acid. Creatine phosphate provides instant energy. It works directly on ADP to make creatine and ATP. But like a battery, it is quickly drained. Ten to 15 seconds of vigorous muscle activity can convert all the creatine phosphate to creatine. Once exhausted the creatine battery will be recharged only when muscle has excess energy.
If the demand for ATP isn't fully met by creatine phosphate, aerobic metabolism (combustion of fuel with oxygen to make carbon dioxide and water) kicks in. During the 10-15 seconds of creatine phosphate metabolism, heart rate and breathing group, increasing supply of oxygen to muscle. This muscle oxygen is used to combust fuels and maintain the ATP supply.
Fat in the muscle is burned exclusively aerobically, providing a high yield of ATP. Aerobic metabolism also uses carbohydrate stored in muscle (glycogen) as a fuel. The glycogen can be broken down to sugar and burned. Carbohydrate and fat combustion both yield a large amount of ATP, though fat yields more than carbohydrate does. If the demand for work keeps going up, these high-yielding ATP sources will eventually reach their limit because the oxygen will become limiting.
At the same time that aerobic metabolism of fats and carbohydrate is taking over the energy supply, some carbohydrate is going down another energy pathway, the glycolytic pathway. This path gives a lot less ATP for every sugar molecule broken down, but it isn't dependent on the oxygen supply. And it makes a waste product called lactic acid.
Muscles are energy efficient. Aerobic metabolism of fat and carbohydrate operates in preference to glycolytic metabolism, as long as there is sufficient oxygen. If ATP demand exceeds what aerobic metabolism can supply, then carbohydrate breakdown increases and the glycolytic route expands to provide the ATP.
In terms of energy efficiency, glycolytic is a kind of "last resort" ATP supply. Instead of burning the sugar to carbon dioxide and water, glycolysis splits the sugar in two (glycol-sis) and captures just a little bit of the sugar energy. The two halves of the sugar that are left are the lactic acid waste. (Actually, lactic acid is only a waste when muscle is energy limited. When oxygen and energy is plentiful, lactate can be burned for energy or even re-synthesized to sugar and glycogen.)
So here is the picture inside you muscle: you are trying to drive forward over those last two hundred meters to the finish line. Your muscles are willing, they just need the energy. The muscle has no more creatine phosphate, that was gone a while ago. Your heart and lungs are working near their maximum, replenishing oxygen to the muscle as fast as possible. As the stroke rate goes up, ATP is consumed faster and faster and the supply from aerobic metabolism just can't keep up. But you have a great supply of glycogen fuel right there in the muscle. The result: an increasing amount of glycogen gets broken down and flows through the glycolytic path to make ATP. This makes a ton of lactic acid.
Actually, while you were rowing through the middle part of the race, a fair amount of carbohydrate was already flowing to glycolysis, even when aerobic metabolism was not at its maximum. But that lactate was being dumped into the blood and circulated to the liver, kidneys and resting muscles, where it was removed from the blood.
So if you look at lactate concentration in the blood, over most of the race there wasn't much change, even though a lot of lactate was being made and dumped by the muscles. That is because the rest of the body cleared the lactate from the blood about as fast as the muscle dumped it in. But when you started the kick at the end of the race, pushing yourself to the limit, streaking toward the finish line, you saturated your lactate removal system, and the blood lactate went sky high.
As blood lactate concentration rose, it became harder and harder for exercising muscle to dump the lactate. Since it couldn't be dumped, the lactic acid level in the muscle went through the roof.
What's so Bad About High Muscle Lactate? High lactic acid level in the muscle has several negative consequences.
First, it makes it harder to keep glycolysis going, that is, it slows down energy supply to the muscle. It is a principle of chemistry that is harder to turn A into B (for example, sugar into lactate) if there is a lot of B (lactate) already present. In Beverly Hills Cop Eddie Murphy proved how powerful this principal is. Axel Foley used a potato to escape his pursuers by plugging up the exhaust pipe of their car. When they tried to start the car, the exhaust gas couldn't escape, so the system backed up and fuel couldn't flow to the engine. In the same way, a hard working muscle produces lactic acid exhaust. If the muscle can't get rid of it, the lactate will create a back pressure in the muscle that interferes with glycolysis.
The second consequence of high muscle lactate is even worse. Glycolytic exhaust is lactic acid. All living cells are affected by acid level (pH). Cells work fine when the acid level is within a certain range and the body has many mechanisms to keep acid levels within the tolerable range. But when the blood lactic acid levels go really high, the acid content of muscle can shift out of the tolerable range. This can interfere with all kinds of processes, including aerobic metabolism and even muscle contraction. Pain, sever loss of power and even immediate cramping can result.
Finally, it is widely believed that extreme acid levels, associated with forced lactic acid production, can damage muscle cells. This is mostly microscopic damage/leakage into the blood of proteins that belong inside the cell, changes in the permeability barriers that cells use to regulate their chemistry, things like that. Many people complain of muscle soreness and cramping in the days following really hard workouts or all-out competitive races. What they are probably experiencing is he body repairing this kind of damage, as well as repairing macroscopic damage like pulled tendons or muscles. (Since it only takes a few hours of rest for the high muscle lactate to return to normal, the next day soreness is from the residual damage, not from lactate still left in the muscle.)
In summary, as you make demands on your muscles to propel you through the water, your muscles use the most efficient energy sources that are available. First they consume their instant energy battery, creatine phosphate. Then, as the heart and lungs get up to speed, they use aerobic metabolism to burn fat and carbohydrate to make ATP. At the same time, some of the carbohydrate gets shuttles down the glycolytic path, making only a little ATP and creating lactic acid waste. The waste lactate gets dumped in to the blood, where it circulates to organs that clear it out. But when you push yourself to the maximum, you make lactate faster than it can be cleared from blood and it builds up. This backs up the muscles glycolytic metabolism and the muscle has a hard time keeping going, mainly due to acid buildup.
How Does This Relate to my Training? The dilemma of the coach who wants to prepare the crew for a race is that rowing requires both high aerobic and anaerobic performance. Dr. Fritz Hagerman has found that a typical 2000-m race is about 75% aerobic and 25% anaerobic. Unfortunately, intense anaerobic conditioning can reverse aerobic performance while training for aerobic capacity doesn't improve anaerobic performance very much (though it does increase the amount of work that can be done before severe anaerobiosis sets in.) The coach's problem is to balance aerobic and anaerobic conditioning to get both to a peak level.
Usually, good aerobic performance is what gets you into the race allowing you to cover most of the course staying with the competition or even pulling ahead. After the first 15 seconds, it is the aerobic systems that provide most of the energy for the entire race.
The anaerobic kick at the end of the race is where tolerance of high lactic acid levels carries the day. Some rowing coaches have said that the last seconds of the race are the time when rowers go into a unique state. They are in pain, their muscles are telling them to slow down, but their desire to win keeps them going, not dropping the stroke rate. Physiologically, this is the time when muscles are working flat out to supply ATP, to dump lactic acid and to fight the negative signals coming from high acid levels, possibly including some cellular damage.
How can Lactic Acid Measurement Help You? Lactic acid measurements can guide you to the most efficient aerobic conditioning it can also let you monitor your aerobic fitness during the competitive season and it may even provide a warning for the onset of anaerobic overtraining while there is still time to correct it.
Building aerobic capacity takes a long time. That's why coaches want you to keep doing those long slow, aerobic pieces during the off-season. Anaerobic conditioning takes less time, but after a certain point, it reverses the benefits of aerobic conditioning.
Whether conditioning is aerobic or anaerobic depends mainly on pace. At low to moderately hard paces, the body is mainly stimulated to increase its aerobic capacity. The harder you work, the more you go from aerobic to anaerobic stimulus. Typical aerobic conditioning involves long, relative slow sessions that can be repeated every day. Anaerobic conditioning uses short, intense repetitions that take your body to its limit. You must allow for adequate rest following anaerobic workouts to allow for repair.
A key pace at the transition from aerobic to anaerobic conditioning is the lactate threshold pace, see Figure 1. This pace is the highest exertion level where the production of lactic acid by muscle is just balanced by lactate removal in the rest of the body. At this pace, you get the most efficient aerobic conditioning, that is, you get the maximum stimulus to build aerobic performance without suffering from high, potentially damaging levels of lactic acid. Also this key pace changes upward in response to effective conditioning and shifts downward when you stop training or start to suffer from overtraining. Therefore, it can be used to monitor the effectiveness of your conditioning program.
At paces up to the lactate threshold, continuous effort gives blood lactate profiles like the two bottom curves in Figure 1. At these paces, blood lactate level will be constant or will fall slowly over time. At or below the threshold pace, you can maintain your effort for a very long time (hours), potentially, for as long as your body has fuel. But when exertion exceeds the threshold, blood lactate begins to rise continually, as shown in the top four curves. How fast lactate rises depends on how high you exertion is above the threshold. And as the Figure shows, whenever exertion exceeds the threshold, there is only a limited time that the effort can be maintained before an inhibitory level of blood lactate is reached and you have to slow down the higher the exertion, the shorter the time.
The sports and scientific literature are full of articles on how to optimize your training and conditioning using knowledge of your lactate threshold. In general, these articles teach that training at your lactate threshold gives the most improvement in aerobic performance for the training hours spent. Therefore, knowing you lactate threshold is particularly useful to people with limited training hours who want optimum results. Also, these articles often refer to the threshold pace as a benchmark from which to gauge other training paces. Exactly what paces you use in your training, and how often you work out, however, depends on your training objectives. Obviously, you train differently for a 6000-m race than for a 1000-m race.
The trouble with these articles is that up until 1997, most people did not have a simple, affordable means to measure their lactate threshold. These training articles usually recognized this and provided various tips and tricks to let you guess your lactate threshold pace. But lactate measurement is the only way to find your true lactate threshold.
Actually determining lactate threshold involves performing a set of workout (for rowers this is usually a set of 5-minute pieces on a Concept II), and taking a finger prick blood sample after each piece to find the blood lactate level. The exertion for the first piece is easy, and you increase the exertion level for each successive piece, reaching hard to very hard for the last one. The results of the lactate analysis are plotted against a quantitative measure of exertion level (pace), such as your speed (split time) or your work level (ergs). This plot is used to find the pace where lactate begins to really build up. The first time that you do the test, the threshold is taken as the pace where blood lactate level reaches 4mM. On Figure 1, the data for the lactate threshold curve would be found if you drew a vertical line at the 5-min point on the time axis and read the lactate levels where this line crosses the different exertion curves. The threshold plot that you would get by plotting these lactate values against the exertion levels is shown in Figure 2.
From Figure 1, you can see that if you workouts were shorter than about 4 minutes, i.e., if you looked at the blood lactate values after four minutes of effort, the lactate levels would be bunched together. In any case, at times up to 4 minutes, lactate levels change rapidly and do not portray the steady progression that is seen after 5 minutes. During those 4 minutes, the body is still bringing aerobic metabolism into play, dividing the ATP supply job to fat, carbohydrate and glycolysis, as well as bringing the lactate removal systems up to speed. If you workouts were longer than 5 minutes, you will get a different set of lactate values except at the threshold pace. (At the threshold pace, blood lactate will hold steady for hours.) And even though the longer workouts shift the appearance of the threshold curve, any test set with workouts longer than about 4 minutes can be used to find the threshold. (We recommend 5 minute workouts).
Of course, you could do a set of 5-minute workouts all at one pace and see if you lactate level was rising or steady. This would be comparable to a single exertion curve in Figure 1. As you see in that Figure, if your exertion level is at or below your threshold, the blood lactate level will hold steady or fall. But if your pace is above your threshold, blood lactate level will go up with each successive workout. This kind of test is the most sensitive way of testing whether an exertion level is above or below your current threshold, but it doesn't tell you how far above or below you are.
There are two products on the market that let you make lactate threshold measurements. LacTest I, a lactate threshold kit, and Accusport a lactic acid strip and meter device. The LacTest I kit provides everything that you need to find your lactate threshold instructions on setting up your test exercises, lancets, gauze pads and a device to collect and stabilize your blood lactate sample with LacTest you perform the test exercises, collect your blood samples and send them back to the LacTest laboratory for analysis. The laboratory will send you a full report, including your threshold plot, a determination of your threshold and training suggestions. With the Accusport meter, you do your own lactic acid measurements, plot your own data, find your own threshold and determine how to use this information in your training program.
In addition to finding your true lactate threshold, both products can be used to optimize and monitor your conditioning. First, keeping track of changes in your threshold over a training season will help you to find the training platforms that work the best to improve your aerobic conditioning and that correlate with your best rowing performance. Some coaches also use these tests to follow anaerobic condition by determining the maximum lactate concentration that a rower can generate and tolerate. (But this approach must be used cautiously, since it isn't simple to sample the true maximum lactate, and in any case, the maximum lactate that is tolerable can vary a lot, person to person, due to genetic heritage).
And finally, these products can determine a parameter called lactate clearance. Lactate clearance measures the rate at which lactate is removed from the blood after lactate production has stopped. There is new interest in this parameter because it is believed that downward changes in lactate clearance may signal the onset of overtraining. If this perception proves true, then lactate clearance measurements may be the coach's best means to detect overtraining while there is still time to correct it.
Now that lactate measurement has become simple and affordable, any coach or individual rower can start to sue the science of performance to benefit their own competitive rowing.
* * * * * *
