Anaerobic Threshold: Myths & Misconceptions

During the last nearly 50 years, the blood lactate curve and lactate thresholds (LTs) have become important in the diagnosis of endurance performance. However, there are many misconceptions which have lead to misunderstanding in the research literature. Lactate Threshold (LT) is the point at which body converts over from using the Aerobic energy system to the Anaerobic Glycolysis energy as the primary source of energy production. In sports involving running activities, it can also be defined as the fastest running speed at which blood lactate levels remain in a relative steady state.

Introduction

During the last nearly 50 years, the blood lactate curve and lactate thresholds have become important in the diagnosis of endurance performance. However, there are many misconceptions which has lead to misunderstanding in the research literature. Lactate Threshold (LT) is the point at which body converts over from using the Aerobic energy system to the Anaerobic Glycolysis energy as the primary source of energy production. In sports involving running activities, it can also be defined as the fastest running speed at which blood lactate levels remain in a relative steady state.

The terms “lactate threshold,” “anaerobic threshold,” “aerobic threshold,” “lactate turn point,” “onset of blood lactate accumulation (OBLA),” and “maximal lactate steady state (MLSS)” are used somewhat interchangeably, although precise definitions may be quite different. Originally, LT was defined as a fixed lactate reading at 4.0 mmol/L, but more recent research has shown that lactate levels at LT can vary as much as 6 mmol/L, between 2 and 8 mmol/L (Beneke, 2000). The lactate threshold is dependent on many factors relating to the production and clearance of lactate. This interaction is what governs the amount of lactate in the blood and ultimately the LT (Billat et al., 2003).

It is important to note that we are measuring blood lactate when defining LT, not muscle lactate. That means that LT is dependent not only on how much lactate a muscle produces but how much actually makes it into the blood stream. When lactate is produced it can either stay in the muscle, travel to adjacent muscle fibers, move into the interstitial space between muscles, or travel to the blood stream. How much travels to the blood is partially dependent on both the difference between lactate levels in the blood and muscle and on the lactate transporter activity. Lactate appearance in the blood also depends on exercise intensity and the amount and type of muscle mass activated. The greater the intensity means a greater reliance on Glycolysis without as much aerobic respiration taking place. Also, the more intense an effort, the greater amount of Fast Twitch fibers are recruited, which because of their characteristics are more likely to produce lactate.

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Lactate Threshold & Role in Sport

The LT measurement is very valuable as it is one of the more sensitive indicators of fitness levels in sport. For example, if training is ineffective the LT will be reached at a relatively low running speed; whereas with more effective training LT will be achieved at a higher speed. This as you can imagine will significant consequences when relating back to the sport. Elite athletes reach the LT at a much higher running speed than sub-elites, which allows them to run faster for longer. The LT is, once again, a function of effective training and also genetics. Many scientific studies indicate that the LT is now one of the best predictors of distance running performance.

The LT is also very valuable relative to training and competition. Training at the threshold has been found to improve performance and the capacity of the aerobic system. Extensive interval training using tempo runs is a typical training modality to improve LT levels. The LT for most males is between 160 and 175 beats per minute, with females being slightly higher, at about 170 to 185 beats per minute. Of all the measurements obtained during testing, the speed and heart rate at which the lactate threshold is obtained are probably the most important to remember when planning training.

For comparison purpose, in competitive University and national level distance runners, the LT is reached at speeds of 6:00 to 5:00 pace per mile. A higher speed at the threshold is desirable. The threshold represents a point where the accumulation of metabolites (e.g. H+) detrimental to performance may begin; thus, a faster threshold speed indicates that the athlete may perform at this speed for a fairly long period of time (possibly up to a marathon) without experiencing undue fatigue. However, when speed or workload exceeds the threshold, the accumulation of by-products and depletion of muscle fuels can lead to more rapid fatigue and a slowing of pace.

The lactate threshold is perhaps the best and most sensitive indicator of distance running performance. An individual who reaches the threshold at a speed of 10 mph (16.1 km/hr) would most likely defeat an individual who reaches the threshold at any lower running speed. It is thus desirable to increase the speed at which the threshold is obtained; this can be accomplished by methods outlined below.

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Training Methods to Improve Lactate Threshold

1) Training at speeds/heart rates near or at the threshold

Training at a given heart rate zone is probably the most effective method for monitoring training intensity relative to the threshold. This has been shown to improve training effectiveness as training near or at the threshold provides a very effective stimulus for improving factors associated with endurance performance.

For example, it was found that when highly-trained distance runners added a weekly 20 min run at the lactate threshold the speed at which the threshold was reached increased after 14 weeks of such training (Sjodin et al., Eur. J. Appl. Physiol. 49:45, 1982). This research also demonstrated that the addition of this single weekly run significantly improved many of the enzymes, which produce energy in muscle. Thus, steady-state training (i.e., longer distance, continuous runs) at the lactate threshold will improve the metabolic capacity of skeletal muscle even in well-trained athletes. It was also found that the addition of the 20 min run improved running economy. Thus, relatively long-duration runs (15-30 min) at the speed or heart rate of the LT should be considered when designing an effective endurance training program for long distance runners. This should be appropriately modified for games based players e.g. Soccer and Rugby player.

The “theory” behind these adaptations is that at a speed greater than the LT, by-products such as Hydrogen ions (H+) begin to accumulate in the muscle. The accumulation of these by-products then results in a slower running speed and/or shortens the length of the workout where a high speed is attained. By keeping training intensity at the LT, the muscle and cardiovascular system can be optimally stressed for a relatively long period of time. In other words, the LT appears to be the “green zone” of training intensity; going above this workload results in fatigue, while going below it does not adequately stress the systems involved. It is this “stress” on the cardiovascular and muscular systems, which provides the stimulus for positive adaptations to occur. Such adaptations then lead to enhanced performance in sport.

2) Interval work

Relatively high-intensity, short rest period interval work has also been found to improve the lactate threshold. Cycles of 3 minutes of work with 1-2 minutes of rest have been found to reduce lactate accumulation during exercise. As with VO2max, the principal is that skeletal muscle and the heart adapt when the level of exercise is close or above VO2max. Unfortunately, this is quite intense exercise, which cannot be maintained for a long period of time (5-15 minutes) due to the accumulation of by-products associated with Glycolysis. Lactate diffuses out of the skeletal muscle by allowing a “recovery” period of walking or slow running between intense work bouts. Intervals thus allow a high workload to be maintained over a longer time period which results in maximal adaptations. With shorter, intense intervals, the stress is even greater. The endurance athlete and coach should thus not shy away from the performance of relatively “sprint” type work with an active recovery between each bout. Such work has been found to increase the lactate threshold, which is a very sensitive and accurate indicator of performance potential in endurance events.

Knowledge about the lactate threshold can also help in designing workloads/heart rates for various types of training. See general recommendations (Coen et al., Int. J. Sports Med., 12:519-524, 1991). Implementation of these guidelines may help prevent overtraining and staleness and also provide a maximal stimulus to the muscle and cardiorespiratory systems for development. Keep in mind that these recommendations are based upon treadmill data under room conditions; different environmental conditions (i.e., heat) and terrain (hills) can alter the relationship and significance of findings.

1) Overdistance runs and “easy” or recovery days should be performed at 80 to 90% of the lactate threshold

2) Intensive, continuous distance runs (15-30 min duration) can be performed at approximately 100% of the lactate threshold, as discussed above. No more than one of these workouts should be performed per week

3) Longer interval work (i.e., 800-1000 m repeats) should be performed at approximately 110-120% of the lactate threshold

4) For shorter, intense interval work the lactate threshold is usually not considered. Keep in mind that such work, although commonly considered “anaerobic” can maximally stimulate the aerobic systems if adequate sets are performed with rest between the sets

This discussion has emphasized the importance of the lactate threshold to the endurance athlete. A key question for the coach/athlete is how to monitor if the threshold is changing over the course of a month or years over training. Unfortunately, measuring the lactate threshold can only be effectively performed in a laboratory setting. New research needs to look at methods of estimating the lactate threshold without having to use the laboratory setting. These will significantly advance the practical application side from a coaching perspective as well as allowing the coach to make more informed decisions in terms of program design and intervention strategies.

This article was written by EPI CEO Karl Gilligan

Written by Karl Gilligan

Founder & CEO 

Elite Performance Institute (EPI)

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