Aerobic and Anaerobic Threshold

Definition 

The aerobic-anaerobic threshold or lactate threshold describes the highest possible load intensity that an athlete can perform while maintaining a state of equilibrium between lactate formation and lactate breakdown. At this point, the athlete reaches the so-called maximal lactate steady state (MLSS) (1, 2). 

Various designations, as well as measurements, for the transition of aerobic to anaerobic energy metabolism, have evolved in the past. The simplest overview represents the three-phase concept according to Skinner and McLellan (4):

  1. Aerobic phase (phase 1)
  2. Aerobic-anaerobic transition phase (phase 2)
  3. Anaerobic phase (phase 3) 

The three-phase nature of energy provision

The three-phase nature of energy provision summarizes the change in the measurement parameters of oxygen uptake (VO2), blood lactate concentration (LA), carbon dioxide output (VCO2), and ventilation (VE), and divides them into the three phases that build on each other:


Abbildung 1

From Figure 1, it can be seen that there is a linear relationship between oxygen uptake (VO2) and exercise. VO2 and also heart rate increase until they reach their respective maximum. 

The lactate (LA) has a very prominent lactate power curve during exercise. Two changeover points are clearly found, described by Hofmann et al. (1997) as "Lactate Turn Point 1" (LTP1) and LTP2. By definition, LTP1 is the first rise in lactate above the resting value and LTP2 corresponds to the MLSS (5).

Carbon dioxide output (VCO2) increases from phase 2 because the body has to metabolize more oxygen than before. 

Respiration/ventilation (VE) also continues to increase from phase to phase to intercept acidosis, through the generation of H+ ions. H+ ions, along with lactate, are the waste product of lactic acid fermentation and are the cause of low pH in the muscles. The entire organism is no longer able to oxidatively metabolize the lactate produced by the working muscles (6).

In the table below, we can see how strenuous the individual phases are based on the Borg values and the percentage distribution of the maximum oxygen uptake as well as the maximum heart rate. Phase 2 is divided again into the LTP1 and LTP2 because it makes a difference, whether one is at the lower or upper limit of the threshold.

Phase 1Phase 2Phase 3
LTP 1LTP2
Borg-SkalaSehr sehr leicht (1 – 3)Leicht (4 – 5)Moderat (6 -7)Schwer > 8
VO2max45 – 55%55 – 70%70 – 80%> 80%
HFmax6 – 70%70 – 80%80 – 90%>90%
Tabelle 1: Drei-Phasen Modell mit modifizierten Bereichsangaben (modifiziert nach Binder et al. 2008) (3)

Energy supply in the three phases

Aerobic energy supply 

Aerobic energy supply is used during long endurance sessions, such as slow endurance runs or LIT sessions on the bike. In sessions characterized by low effort and high repetition frequency, the slow-twitch (endurance) muscle fibers are used. They are also referred to as type S (slow) fibers. 

During aerobic energy production, the body has enough oxygen available to produce adenosine triphosphate (ATP) from fats and carbohydrates. ATP is the basis of metabolism and is therefore elementary for muscle contraction. The metabolism of ATP releases energy and allows the muscle to perform its mechanical work. 

ATP → ADP + P (+ energy).

With the help of creatine phosphate, the body is able to convert the created ADP again into energy-rich ATP and thus provide for enough energy in the aerobic zone. 

ADP + creatine phosphate ↔ ATP + creatine

Lactate is also already formed under aerobic energy provision. However, there is not yet a rise in lactate here, as it can be metabolized by the body.

Aerobic-anaerobic energy supply

The aerobic-anaerobic transition area (phase 2) represents the overlapping energy-providing processes.
In this phase, a higher performance is demanded from the body, which cannot be covered only by the aerobic energy supply. There is a rise in lactate in the blood, indicating that as aerobic glycolysis increases, so does anaerobic glycolysis. Glycolysis describes the biochemical process of breaking down glucose to pyruvate. 

In addition, it can be seen that the respiratory quotient (RQ) increases and approaches 1.0 as the load increases. If the RQ is at 1.0, it means that energy is obtained exclusively from carbohydrates (7). If the RQ value is between 0.8 - 0.85, proteins are metabolized more and from 0.7, fats are metabolized. 

As intensity is further increased, despite further increases in elimination and buffering, increasing lactate production reaches a point where production and buffering just balance each other (maximal lactate steady state).

Aerobic-anaerobic energy supply 

In anaerobic energy provision, glucose is metabolized to pyruvate under low-oxygen conditions to produce ATP. This process also produces the by-product NADH and H+ ions, which are ultimately responsible for the acidification of the muscles (low pH value). The decreasing pH value is ultimately responsible for the fact that a performance has to be stopped at some point.

Training control and improvement of the aerobic-anaerobic threshold

For a sensible training control, the exact determination of your threshold power is absolutely necessary, since your intensity ranges are aligned according to it. Your aerobic-anaerobic threshold should be analyzed in a performance diagnostic under laboratory conditions. Otherwise, it is also possible to complete an FTP test on the roller. Here it is important to note the exact test protocol so that a comparison to already existing tests is possible. 

From the point of view of training control, the aerobic-anaerobic transition zone (phase 2) is of particular importance. In endurance sports, it is usually desired to shift the aerobic-anaerobic threshold as far as possible to the right. However, this is completely dependent on the respective competition distance. A rightward shift of the lactate power curve means that the athlete is able to maintain a relatively high and constant power output for as long as possible without experiencing a large lactate increase in the muscles. To achieve this, it is important to increase the maximum oxygen uptake so that the working muscles have as much oxygen available as possible. How you train the maximum oxygen uptake, you can read our article on VO2max. In addition to increasing VO2max, it is important to keep the counterpart of the maximum lactate formation rate (VLamax) low. The VLamax describes how much lactate your body can produce within a period of time. This amount of lactate is then expressed in mmol/l/s (millimoles per liter per second). In short, VLamax training aimes to make the fast muscle fibers (type F(fast) fibers) work economically. Typical training variants here are strength endurance intervals on hills or the classic threshold training.

Sources

  1. Binder, R. K., Wonisch, M., Corra, U., Cohan-Solal, A., Vanhees, L., Saner, H., Schmid, J. P. (2008). Methodical approach to the first and second lactate threshold in incremental cardiopulmonary exercise testing. European Journal of Cardiovascular Prevention and Rehabilitation. 15. 726-734
  2. Faude, O., Kindermann, W., Meyer, T. (2009). Lactate Threshold Concepts. Sports Medicine. 39(6), S. 469–490.
  3. Hofmann, P., Pokan, R., Von Duvillard S. P., Seibert, F. J., Zweiker, R., Schmid, P. (1997). Heart rate performance curve during incremental cycle ergometer exercise in healthy young male subjects. Med Sci Sports Exerc 29(6): 762–768.
  4. Kroidl, R., Schwarz, S., Lehnigk, B. (2015). Kursbuch Spiroergometrie. Thieme.
  5. Pokan, R., Hofmann, P., Wonisch, M., Smekal, G., Bachl, N., Mayr, W., Schmid, P. (2004). Leistungsdiagnostik und Trainingsherzfrequenzbestimmung in der kardiologischen Rehabilitation. Journal für Kardiologie 11(11): 446-452.
  6. Skinner, J. S., McLellan, T. H. (1980). The Transition from Aerobic to Anaerobic Metabolism. Research Quarterly for Exercise and Sport 51. 234-248.
  7. Zintl, F. (1990). endurancetraining. S. 64. BLV: München.

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