Edit article: Optimize endurance training
By Lance Dalleck, M.S. & Len Kravitz, Ph.D



The next article here is somewhat outdated by new developments and insights. Yet placing this article is justified because the subject which is treated clearly explains the principles of training. But the modern insights need to be taken into account. In brief, this involves two points.

  • 1: Lactate is not the cause of the acidosis. Lactate is an important source of energy.
  • 2: The lactate threshold can be replaced by the athlete by the FTP, the Functional Threshold Power, which is much more convenient in practical and financial terms for the athlete.

The article is based on the lactate threshold or the anaerobic threshold as being the best and most consistent predictor of performance in endurance events. Replace the lactate threshold by the FTP and the basic story remains more intact. Two notes:

  1. We now know that the acidosis caused by intense exercise is not caused by an increase in lactate levels (see Article 150). The acidosis is caused by an increase of H + ions or protons, which are released during the hydrolysis of ATP. With increasing acidification lactate levels also increase. As a result, the lactate content remains indirectly a measure of the height of the acidosis. For this reason, the anaerobic threshold may still be used as an initial value in order to establish the level of performance objectively. By means of the lactate curve the exercise intensities of the different levels of exercise are displayed in HF and / or in Watts.
  2. A lactate curve is no longer necessary as the FTP, the functional threshold power, which virtually corresponds to the anaerobic threshold may be performed in an extremely simple manner, bloodless, under sport-specific circumstances by the rider himself. The FTP provides the same information that can be obtained by a lactate test. A lactate test would best be left to professional effort laboratories. But if the athlete has mastered the way of testing and understands how everything works then he will no longer use the expensive time-consuming lactate testing.

The Article


If you want to optimize your endurance training you will discover that the lactate threshold is the best predictor of endurance performance. There is a lot of other terminology that is used for the same physiological event as the lactate threshold. Like the ventilator threshold, anaerobic threshold,

the OBLA = onset blood lactate accumulation and deflection point.

The purpose of this article will be to clearly describe the physiological mechanisms behind the lactate, ventilatory and anaerobic threshold, as well as discuss the heart rate threshold. This knowledge will be used to outline training principles for the improvement of the lactate threshold values.


The maximal oxygen uptake (VO2max) always was the key component to success in prolonged endurance exercises.  However more recently researchers have proposed that the lactate threshold is the best and most consistent predictor of performance in endurance events. Research studies have repeatedly found high correlations between performance in endurance events such as running and cycling and the maximal steady state workload at the lactate threshold.


At rest and under steady-state exercise conditions, there is a balance between blood lactate production and blood lactate removal. The lactate threshold refers to the intensity of exercise at which there is an abrupt increase in lactate levels. Key mechanisms for the lactate thresholds:

  • A decreased lactate removal
  • An increased fast-twitch motor recruitment
  • An imbalance between glycolysis and mitochondrial respiration
  • A low oxygen content in blood
Maximal lactate steady state. Lactate = 3.6, HR = 172, Running speed = 4.2m/s. There is a balance between blood lactate production and blood lactate removal. Next step there is an abrupt increase in lactate levels.

A metabolic pathway is a series of chemical reactions that will result in the formation of ATP and waste products like carbon dioxide. The three energy systems of the body are:

  • ATP-PC system also called the Phosphagen System
  • The glycolysis, the breakdown of sugar
  • The mitochondrial respiration, the cellular production of ATP in the mitochondrion.

ATP – PC is the simplest energy system of the body with the shortest capacity, up to 15 seconds, to maintain ATP production. During intense exercise, as in sprinting, the ATP-PC is the most rapid and available source of ATP.

During submaximal endurance exercise, the energy for muscle contraction comes from ATP regenerated almost exclusively through mitochondrial respiration, which initially has the same pathway as glycolysis. It is a misconception to think that the body’s energy systems work independently. In fact the three energy systems work together cooperatively to produce ATP.

Through glycolysis, blood glucose or muscle glycogen is converted to pyrovate, which once produced will either enter the mitochondria or be converted to lactate depending on the intensity of exercise.

Pyruvate enters the mitochondria at exercise intensity levels below the lactate threshold, while at exercise intensity levels  above the lactate threshold the capacity for mitochondrial respiration is exceeded and pyruvate is converted to lactate. It is at this point that high-intensity exercise is compromised, because the glycolytic and phosphagen energy systems that are sustaining the continued muscle contraction above the lactate threshold can provide ATP at a high rate, yet are only capable of doing so for short duration of time.

So, the energy for exercise activities requires a blend of all energy systems.  However, the determinants of the involvement of the particular energy system are highly dependent on the intensity of the exercise. Mechanisms contributing to the lactate threshold:


Lactate has long been seen as a harmful substance originated exclusively during intense exertion. But the production of lactate is not harmful at all.

Even at rest a small degree of lactate production takes place, which indicate there must also exist lactate removal or else there would be lactate accumulation occurring at rest. The primary means of lactate removal include its uptake by the heart, liver and kidneys as a metabolic fuel.

Within the liver lactate functions as a chemical building block for glucose production, known as gluconeogenesis, which is then released back into the blood stream to be used as fuel elsewhere. Additionally, non-exercising or less active muscles are capable of lactate uptake and consumption. At exercise intensities above the lactate threshold, there is a mismatch between production and uptake, with the rate of lactate removal apparently lagging behind the rate of lactate production.


At low levels of intensity, primarily slow-twitch muscles are recruited to support the exercise workload. Slow-twitched muscle is characterized by a high aerobic endurance capacity that enhances the energy metabolism of the mitochondrial respiration energy system. Conversely, with increasing exercise intensity there is a shift towards the recruitment of fast-twitched muscles, which have metabolic characteristics that are geared toward glycolysis.  The recruitment of these muscles will shift energy metabolism from mitochondrial respiration towards glycolysis, will eventually lead to increased lactate production.


At increasing exercise intensities, there is an increase reliance on the rate in the transfer of glucose to pyruvate through the reactions of glycolysis. This is referred to as glycolytic flux. As described before, the pyruvate produced at the end of glycolysis can either enter the mitochondria or be converted to lactate. There are some researchers who believe that at high rates of glycolysis, pyruvate is produced faster than it can enter into the mitochondria for mitochondrial respiration. Pyruvate that cannot enter the mitochondria will be converted to lactate which can then be used as fuel elsewhere in the body, such as the liver or other muscles.


For years, one of the primary cases of lactate production was thought to include low levels of blood flow (ischemia) or low levels of blood oxygen content (hypoxia) to exercising muscles. This led to the term anaerobic threshold, which will be discussed in more detail shortly. However there is no experimental data indicating ischemia or hypoxia in exercising muscles, even at very intense bouts of exercise.

Unfortunately and confusing, the lactate threshold has been described with different terminology by researchers, including maximal steady-state, anaerobic threshold, individual anaerobic threshold, lactate breaking point, deflection point and onset of blood lactate accumulation. Whatever reading on the topic of lactate threshold it is important to realize that these different terms are essentially describing the same physiological event.


As exercise intensity progressively increases in intensity, the air into and out of your respiratory tract, called ventilation, increases linearly or similarly. As the intensity of exercise continues to increase, there becomes a point at which ventilation starts to increase in a non-linear fashion.  This point where ventilation deviates from the progressive linear increase is called the ventilator threshold. The ventilator threshold corresponds, but is not identical, with the development of muscle and blood acidosis. Blood buffers, which are compounds that help to neutralize acidosis, work to reduce the muscle fibers acidosis. This leads to an increase in carbon dioxide, which the body attempts to eliminate with the increase in ventilation.


The term anaerobic threshold was introduced in the 1960´s based on the concept that at high-intensity levels of exercise, low levels of oxygen or hypoxia, exists in the muscles. At this point, for exercise to continue, energy supply needed to shift from the aerobic energy system, the mitochondrial respiration, to anaerobic energy systems; glycolysis and the phosphagen system.

There are many researchers who strongly object to the use of the term anaerobic threshold, believing it is misleading. The main argument against using the term anaerobic threshold is that it suggests oxygen supply to muscles is limited at specific exercise intensities. However as mentioned previously there is no evidence that indicates muscles become deprived of oxygen – even at maximal exercise intensities.

The second main argument against using anaerobic threshold is that it suggests at this point in exercise energy, metabolism shifts completely from aerobic to anaerobic energy systems. This interpretation is an oversimplistic view of the regulation of energy metabolism, as anaerobic energy systems; as glycolysis and phosphagen system, do not take over the task of ATP regeneration completely at higher intensities of excerise, but rather augment the energy supply provided from mitochondrial respiration.


In the early 1980´s, Conconi developed the methodology to detect the lactate threshold through a running test by determining the heart rate deflection point. This easy and non-invasive approach to indirect lactate measurement has been utilized extensively for training program design and exercise intensity recommendations. However, some research has shown that the heart rate deflection point is only visible in about half of all individuals and commonly overestimates lactate threshold. Because of these findings, and the grave errors associated with its use, personal trainers and fitness professionals are discouraged from recommending the heart rate threshold method when designing training programs for athletes.



In summary, ventilatory and lactate thresholds, although very similar, should not be viewed as occurring at precisely the same exercise workloads. The use of the term anaerobic threshold in the lay community and with exercise professionals has led to much confusion and oversimplification of the body’s energy systems. So much error presently exists with the heart rate threshold technique that further research is needed to be able to confidently utilize this technique. Therefore, the focus of designing a successful endurance training program will be based upon the physiological understanding of the lactate threshold.


It is well known that following endurance training, the lactate threshold will occur a higher relative percentage of an individual´s maximal oxygen uptake (VO2max) than prior to training. This training adaptation allows for an athlete to maintain higher steady state running velocities or cycling workloads, while maintaining a balance between lactate production and removal. Endurance training influences both the rate of lactate production and removal.

The reduced lactate production, at the same given workload, following endurance training can be attributed to increased mitochondria size, mitochondrial numbers and mitochondrial enzymes. The combined result of these training adaptations is an enhanced ability to generate energy through mitochondrial respiration, thus lowering the amount of lactate production at a given workload.

In addition, endurance training appears to cause an increase in lactate utilization by muscles, leading to a greater capacity for lactate removal from circulation, despite the heightened lactate production rates occurring at high levels of exercise intensity, blood lactate levels will be lower.

It should be noted that endurance training may also improve capillary density around the muscles, especially the slow-twitch muscles. This adaptation improves blood flow to and from exercising muscles, which will enhance the clearance of lactate and acidosis.

Some important articles claimed that professional high level cyclists, such as Bradley Wiggins, Chris Froome and Fabian Cancellara are capable of exceptional performance because they are able to withstand very high lactate levels. This assumption is not correct. Their blood lactate levels remain low, even while delivering peak performance.


Although the optimal training for lactate threshold improvement has yet to be fully identified by researchers, there are still some excellent guidelines you can follow in generating training programs and workouts in order to enhance the lactate threshold levels of athletes. Research has indicated that training programs that are a combination of high volume, interval and steady-state workouts have the most pronounced effect on lactate threshold improvement.


The best way to improve the lactate threshold levels of your athletes is to simply increase their training volume, whether their endurance activity is cycling, running or swimming. Increased training volume should be gradual and in the order of approximately 10-20% per week. For example, if an individual is currently running 20 miles per week, the increase in training volume should be 2-4 miles per week. While this approach may appear conservative, it will help to prevent over training and injuries. Additionally, intensity during this phase of training, when volume is being steadily increased, should be low. The maximum training volume an individual attains is dependent on numerous factors and can be best gauged by determining the overall physical capacity and motivation of your athlete. Factors such as training status, age, body weight, and training time will all determine the training volume your athlete  is realistically capable of achieving. The premier benefit of increased training volume is an increased capacity for mitochondrial respiration, which, as mentioned earlier, is imperative to improvements in lactate threshold.


Following an adequate build-up in training volume, the next aspect that should be addressed is interval and steady-state training. Correct training intensity during this phase, which will be focused around an individual’s lactate threshold, is key to the continued success of your athlete’s training program. The methods used for monitoring interval and steady-state training must ensure that intensity is not being under-estimated or over-estimated.

Most athletes do not have the opportunity to have their lactate threshold determined in an effort laboratory, with the aid of a maximal lactate test with blood sampling. Therefore, there are a number of good non-invasive methods whereby the lactate threshold can be estimated.

One of these methods makes use of the percentage of the heart rate reserve, HRR. In trained athletes the lactate threshold is between 80-90% of HRR. In untrained individuals the lactate threshold is between 50-60% of HRR.

Another method uses the Rating of Perceived Exertion, RPE. That is an accurate way to determine the training intensity during steady state and interval training. Lactate threshold occurs between 13 and 15 on the RPE scale, which correspondents to feelings of ‘somewhat hard’ and ‘hard’.

Other methods are:

  • Maximum heart rate
  • Karvonen
  • Threshold HR
  • Functional Threshold Power, FTP
Lactate threshold is the point at which lactate increases in the blood stream exponentially. FTP is the maximum effort an athlete can maintain for one hour. So lactate threshold and FTP are not the same.

Steady-state workout sessions should be performed as close as possible to the lactate threshold. The length of these bouts can vary depending on the training status, type of endurance-activity being performed, and distance of endurance-activity. The novice runner, training for 5 km road races, performing his first steady-state run may only do a workout of 10 minutes in duration.

A semi-professional cyclist, training for multiple-days of racing 80-100 miles distances, may complete a steady-state workout of an hour in duration.


Interval training workouts are high-intensity training sessions performed for short durations of time at velocities or workloads above the lactate threshold. Similar to steady-state workouts, interval workout times and distances are dependent on training status, type of endurance-activity being performed and distance of endurance-activity.

The novice runner, training for 5 km road races, may complete three, 1-mile intervals at or faster than race pace, with adequate recovery time between each repeat. The semi-professional cyclist, training for multiple-days of 80 to 100 mile distances, may perform several 5 to 10 mile intervals at, or in excess of, their race pace with appropriate recovery bouts between repeats.

The key to successful steady-state and interval workouts is a careful monitoring of training intensity.  One can use a heartrate monitor and/or a powermeter for that purpose. Steady-state and interval workouts should not exceed approximately 10-20% of total weekly training volume.

The lactate threshold is the most important determinant of success in endurance-related activities and events, and the main goal of endurance training programs should be the improvement of this parameter. This can be accomplished by first focusing on developing training volume, and then the incorporation of steady-state sessions, at the lactate threshold, and interval workouts, above the lactate threshold. Remember that correct training intensity is essential to the success of any endurance-training program.

Utilizing of both the relative percentage of heart rate reserve (HRR) and the rating of perceived exertion (RPE) scale are proven methods for monitoring the training intensity of the athlete during their workouts.




Acidosis: the decrease in pH

Anaerobic threshold: original concept describing increased lactate production during conditions of lack of oxygen in blood flow

Gluconeogenesis: synthesis of glucose from non-carbohydrate sources

Glycolysis: series of steps that breaks down glucose to pyruvate

Glycolytic flux: an increase rate in the transfer of glucose to pyruvate through the reactions of glycolysis

Hypoxia: low levels of blood oxygen content

Ischemia: Low levels of blood flow

Lactate: is manufactured  from pyruvate during higher intensity exercise

Lactate threshold: intensity of exercise at which there is an abrupt increase in blood lactate levels

Metabolic pathway: chemical reactions causing the formation of ATP ans waste products

Metabolism: sum of all energy transformations in the body

Mitochondrial respiration: reactions in the mitochondrion that ultimately lead to the production of ATP and consumption of oxygen

Phosphagen system: production of energy from coupled reactions of ATP and PC

Pyruvate: compound derived from metabolism of carbohydrates

Ventilatory threshold: occurrence in progressive increase in intensity of exercise at which there is a non-linear increase in ventilation.