Understanding Blood Lactate to Optimize Training and Performance
By: Matt Van Dyke
The ability of the body to buffer muscle acidity due to anaerobic energy (ATP) production and the accumulation of hydrogen protons is essentially the rate-limiting step in repeat-sprint abilities, such as those seen in many team sports. Lactate can be used in many ways within the body. When functioning optimally, it allows increased muscle force production for a longer period of time by attenuating a drop in intracellular pH. Lactate clearance and tolerance can be improved with a combination of base endurance, and high-intensity training. Optimal nutrient intake and timing can also be used to increase the ATP production, while lactate allows the continuation of anaerobic-glycolysis.
In the past, lactate has had some negative connotations directed towards it, so I am going to begin this post by dispelling some of these “myths”. The first and most common misunderstanding of lactate is that it is only produced during intense exercise. This could not be further from the truth. It is being created within your body at all times, even while you are seated reading this post. As lactate is produced, it circulates in the blood as a valuable energy source and is preferred by various tissues. You don’t notice lactate is being produced due to your body’s ability to effectively move it around and use it before accumulation occurs. As exercise intensity increases, lactate production increases. At some point in time lactate production exceeds the body’s ability to clear lactate, and accumulation begins to occur. When monitoring blood lactate, this point is called the lactate threshold and can be shifted further to the right with proper training.
As one can see in the figure below, proper training shifts lactate threshold to the right, leading to an increased work capacity at the same amount of blood lactate accumulation prior to training.
The second myth addressed in this post is that lactate is a cause of delayed muscle soreness. At high-intensity training, rapid lactate production has the ability to cause a burning feeling by activating free nerve endings. However, lactate is cleared from the muscle cell within two to four minutes post-training. This rate of clearance from the cell can also be improved with proper training. Lactate accumulation is cleared far too rapidly for it to be a cause of delayed muscle soreness.
The final lactate myth covered in this post, that increases in lactate accumulation causes the muscle cell to become more acidic, is quite possibly the most widely misunderstood aspect of lactate. The actual functional role of lactate is to work as an intracellular buffer and to prevent acidosis within the muscle cell. By preventing a large change in pH inside the cell, lactate has the ability to allow work to continue for a longer period of time before the effects of acidosis on muscle function, and thereby, performance is evident.
Lactate is a Positive for Athletes
As some of the common “lactate myths” are dispelled, one can see how lactate production is actually beneficial for athletes. One positive for athletes is that lactate has the ability to accept hydrogen ions, which contribute to a pH change in muscle, making it an important buffer. With muscular pH being an important limiting factor in repeat-sprint abilities, it is vital to train the body to buffer as effectively as possible. This means athletes involved in repeat-effort sprint bouts, such as many team sports, as well as athletes with multiple competitions within a short time period have the greatest potential to improve through lactate training.
A second benefit to athletes is that tracking the production and accumulation of lactate that appears in the blood helps identify which energy systems are being utilized during training. As intensity of training increases, lactate production increases accordingly, along with an even greater production of hydrogen ions. If these intracellular hydrogen ions are produced too rapidly, the cell becomes acidic, ATP production and intensity is automatically limited.
High-intensity efforts require rapid re-synthesis of ATP. A third positive of lactate for athletes is that the ability of lactate to accept hydrogen ions allows substrates, such as NAD (the key hydrogen carrier during glycolysis), to remain free to continue ATP re-synthesis as rapidly as possible. The body has the ability to increase lactate production and clearance, but not NAD. So if one can generate, clear, and tolerate greater amounts of lactate, more ATP can be re-synthesized and more work can be performed.
The third positive benefit lactate can have for athletes is through the body’s ability to utilize lactate as an energy substrate. Oxidative fibers within the body have the ability to use lactate as an energy source. These fibers include the heart, kidneys, and type I, slow twitch, muscle fibers, with the heart preferring to use lactate as a substrate during exercise. Lactate also is a gluconeogenic precursor in the liver, meaning lactate can be recycled back to glucose and used as a continuing energy source.
The graphic below represents the ability of lactate, once removed from the muscle cell, to be utilized as an energy substrate and a gluconeogenic precursor. When lactate leaves the muscle cell, nearby type I muscle cells have the ability to utilize lactate as an energy source; this is commonly found in mixed muscles. If there are no type I fibers nearby, lactate will continue in the blood stream where it can be picked up by other oxidative fibers such as type I muscle fibers, including the heart, or the kidneys. If lactate remains in the blood and gets to the liver, it can be converted to glucose and stored as glycogen within the liver, or the glucose can be sent back into the blood. In this scenario glucose will be sent to a working muscle that can use the glucose to continue high-intensity activities, whether in training, or competition.
In order for lactate to be utilized in other areas of the body as an energy substrate, the methods in which it is moved in and out of the cell must be understood. Monocarboxylate transporters (MCT’s) are not the only method of lactate transport across a membrane, but they are the main source of lactate uptake or removal from the cells and will be the main focus of this post. Studies show clearly that MCT’s have an inverse relationship with blood lactate levels post-exercise, meaning if MCT concentrations are high, blood lactate levels tend to be low. This demonstrates an increased ability to recover rapidly, with improved lactate clearance rates. There are currently 14 known MCT’s, with only six having known functions. In the case of lactate clearance during exercise, two MCT’s are utilized: MCT1 and MCT4. Each have specific roles but they are important to rapidly move lactate into and out of a cell as well as moving lactate into the mitochondria to be used for ATP production.
MCT1 is found primarily on the cell membrane and mitochondrial membrane of type I muscle fibers and is responsible for the uptake and removal of lactate. With it being located mostly on oxidative fibers, which do not produce much lactate, the main purpose of MCT1 is the uptake of blood lactate and to then utilize it as an energy substrate within the mitochondria. MCT1 has been shown to be quite responsive to specific training.
MCT4 is located mostly on type II muscle fibers, although there is a much larger variation between subjects for MCT4 than MCT1. With MCT4 being primarily found on glycolytic fibers, where the majority of lactate is produced, it is mostly responsible for the removal of lactate out of these fibers and into the blood. MCT4 does show improvements with training, although not to the same extent as MCT1. This clearly demonstrates the body increases its ability to oxidize lactate as an energy source, rather than tolerating it within the glycolytic fibers.
The visual below is an example of a cell and how MCT’s are used to move lactate in and out of a cell. The top left corner of the cell depicts MCT1 and MCT4 located on the cell membrane of a glycolytic fiber. The type II fiber is primarily responsible for the production of lactate through anaerobic glycolysis. The cell must have an ability to remove the lactate being produced, which can be done by either MCT1 or MCT4. The other two MCT1 transporters depicted below are examples of how lactate is brought across the membranes of oxidative fibers from either the bloodstream or nearby type II fibers. MCT1 transporters are the biggest factor in lactate clearance from the blood and also have the largest influence on the ability to utilize lactate as an energy substrate within the mitochondria.
Reasons to Improve Lactate Kinetics
With the positives of lactate being presented in an earlier paragraph, some of the reasons for lactate improvement will now be identified. Other reasons to improve the ability of lactate kinetics, specifically MCT’s remain. The ultimate goals during exercise include buffering hydrogen ions and keeping the ATP:ADP ratio consistent. The energy systems that are responsible for ATP production and re-synthesis can be viewed as fuel tanks, each with their own specific characteristics. The creatine phosphate system (PCr) produces ATP the most rapidly, but has a very small fuel tank, lasting only about 6-10 seconds. The PCr system does not have a major impact on lactate production or clearance, so it will not be a main focus within this post. Anaerobic glycolysis has the ability to produce ATP quickly, with a considerably larger fuel tank than the PCr system. Anaerobic glycolysis produces an end-product, which upon accumulation can limit repeat-sprint abilities. Finally the aerobic system has the largest fuel tank, but this system does not have the ability to produce ATP quickly enough to be the sole energy producer for high-intensity activities. The importance of controlling pH was touched on earlier, specifically in repeat-effort activities. When pH is uncontrolled and the muscle cell becomes acidic, a decline in tension development and subsequent muscle fatigue occurs. The reduced rate of ATP production, with the increased accumulation of hydrogen ions, along with the thought that hydrogen ions compete with active binding sites on sarcomeres, leads to a decreased ability to produce force. The better an athlete is at buffering hydrogen ions during high-intensity exercise the greater their ability to perform repeat-efforts with short rest bouts.
How to Improve Lactate Kinetics
The methods to optimize lactate within the body include base endurance and high-intensity training. High-intensity methods are already widely used by strength coaches, but it is the base endurance training that may possibly be the most pivotal piece to improve lactate kinetics.
Base training builds a foundation for future training, and in this scenario, is any type of repetitive movement that increases blood flow while keeping intensity low. Typically 40-50% of max heart rate is a good target zone, although research is still being completed to determine a more exact range. During this training, the length of the activity is a key determining factor, with the goal being a pace that can be maintained for an hour. This training time can be accumulated in multiple bouts throughout the day; however, a goal should be set where a constant 60-minute bout without a break is achieved. Base endurance training at this intensity increases MCT concentration, particularly MCT1, and also increases mitochondria concentration. These adaptations maximize the ability of the body to clear lactate and then utilize it as an energy substrate, while also improving the aerobic abilities of the athlete. By improving lactate clearance, athletes are better able to recover their PCr stores. As recovery time is decreased for the PCr energy system, ATP availability to the athlete is increased, leading to an increased ability to produce high-intensity efforts. Examples of base training include extended dynamic warm-ups, brisk walking, and single leg stability training. As stated earlier, the effects of base training are cumulative, allowing for the time spent on the training to be broken up without much consequence.
What I have found to work for my athletes is an extended dynamic warm up, brisk walking between exercise sets, and brisk walking as a conditioning piece. Base training can be completed during the same block as general preparatory circuits. Base training also can be completed during high-intensity training as the intensity of the brisk walk is too low to activate type II fibers. This low intensity guarantees explosive fibers will not become more oxidative via aerobic adaptations. I also have supplemented brisk walking as a conditioning piece with teams to ensure each athlete has the necessary foundation to clear lactate optimally during high-intensity training and competitions.
Once the ability to clear lactate has been optimized it is then time to begin high-intensity training. The purpose of this phase is to increase the accumulation of lactate within the working muscles and train “tolerance” of that lactate, which increases the size of the “sink” in the graphic below. I have found the best method of training for high-intensity is the modified undulated program. This program uses the basics of block periodization and prevents any coach from attempting to achieve too many adaptations within a single cycle. Each day has a particular goal based on the intensity and volume of exercises. This method also utilizes timed sets, so energy systems specific to each sport can be optimized each day. With residual effects of around 30 days, the aerobic system can be re-trained during deload weeks to guarantee the desired adaptations of base training are not lost throughout the high-intensity training cycles. The circuits used for general preparatory can be completed again during this time.
High-intensity training methods do not appear to increase MCT concentration, but rather maintain them. This is the reason base training is absolutely necessary for limiting acidosis during repeat-sprint efforts, such as team sports. Extreme training leading to excessive lactate production does have the ability to acutely decrease MCT concentration. These decreases are caused by the “sink” being completely filled and the body preventing extreme pH change. The reduction in MCT concentration leads to a decreased intensity of exercise until the body’s acidity is no longer challenged. Specific running programs such as biometric training can be used to prevent these unwanted pH changes within the cells that can actually hinder training. Biometric training involves a percent drop-off chart and allows a coach to help prevent an athlete from being over, or under trained. This method should be used in small groups to ensure each athlete is timed individually for each rep. Once an athlete reaches the percent drop-off deemed appropriate for the training session, according to their fastest rep that day, their training session is finished.
Nutritional needs to support lactate training
Proper nutrition and nutrient timing are critical for the body to complete the required high-intensity training to peak lactate and to maximize the ability of the body to produce ATP using glycolysis. Proper stores of muscle glycogen allow the continuation of glycolysis. Carbohydrate intake is vital for high-intensity athletes and provides the requirements for muscle glycogen storage, which is the primary substrate for anaerobic glycolysis. With the ability of elite athletes to burn up to 100 grams of glycogen in a quality 400 meter sprint and the body only having the ability to store about 400 grams of glycogen at one time, the importance of proper nutrition to support recovery and training becomes clear. At this rate of usage, an athlete would only have the ability to complete two or three quality 400 meter sprints per day before the body began to feel sluggish.
The four hour window post-training is where the biggest advantage lies for proper recovery from intensive training, particularly for athletes that have multiple competitions within a short span of time. Without proper nutrient timing the body may require up to 24 hours to re-synthesize glycogen content, which many athletes’ event schedules do not permit. Nutrient timing exploits the high-sensitivity of cells to glucose uptake post-exercise and works to increase the rate of glycogen re-synthesis with the use of high-glycemic carbohydrates. Carbohydrates should be consumed at a rate of 1.2 g/kg/hr within this window for optimal glycogen re-synthesis. Protein should be supplemented as well with a ratio of 3:1 or 4:1 of carbohydrate to protein, with the main focus of this recovery stage being to restore glycogen content. A complete, in-depth look at the importance of nutrient timing can be seen in Nutrient Timing for Proper Recovery.
The graphics below represent the pre, and post-combination training described previously, which includes base endurance, high-intensity, and nutrient intake and timing training. As discussed earlier, base training increases MCT concentration, leading to an increased ability of the oxidative fibers to pull lactate from the blood into muscle cells and utilize lactate as an energy substrate. Base training also increases the “tank” size for aerobic energy systems. High-intensity training allows the body to “tolerate” more lactate. This is shown within the graphic as an increase in the size of the “sink”.
As athletes adapt and improve their abilities to train, they will be able to produce increased levels of lactate. The body must adapt to functioning at these higher levels of production. Proper nutrient intake and timing allows for maximal glycogen stores, which, in turn, allows athletes to compete at higher intensities for extended periods of time. It should be noted again that the body on its own does not increase the amount of glycogen it can store, but rather maximizes the storage when optimal nutrient intake methods are used. When these three methods are combined, athletes will have the ability to pull energy out of the “sink” at a faster rate, increase the size of their “sink”, as well as increase their abilities to maintain high-intensities. These will all lead to an increased training status and optimal performance, particularly in team sports with repeat-sprint bouts.
Below is an annual plan for an advanced hockey athlete. During the first phase of the off-season base endurance is focused on to maximize lactate clearance. From there, high-intensity training is completed and continues to become more specific as the season approaches. Base endurance training is also completed during the deload weeks of high-intensity training to maintain the residual effects of base training. This phase finishes with a peaking phase most specific to a sport’s game speed and individual energy system needs.
Lactate can be peaked about every three months. With this time frame in mind, a coach can set up a strength and conditioning program to maximize an athlete’s lactate threshold at pivotal times of the year. In the example provided for hockey, I have chosen to peak this team at the end of the year for the national tournament. Having the knowledge of when I will be peaking my athletes allows me to work backwards through the competition season and set up a progressive plan.
It is your responsibility as a coach to know the intensity of your team’s sport practices. If your athletes are already getting high amounts of high-intensity training with daily sport specific practices they will not need to be trained at those high-intensities as often in the weight room or through conditioning, and base endurance levels should be the primary focus. Base endurance levels of athletes will also determine the amount of time spent on each block, particularly during lactate peaking.