The Merits of Lactate Threshold Testing
Brett Petersen, MS, CSCS – Petersen Performance Lab
In this article I wish to describe the merits of lactate threshold testing. Given that many of you have already had a lactate threshold (LT) test performed by me, have a test scheduled, or will be attending the upcoming March clinic; I wish to provide some information concerning the lactate threshold test and what the derived data can be used for. Finally, I will also explain the concept of maximum lactate steady state (MLSS) and provide information about a pilot study I will be conducting this upcoming race season.
To begin with, I will provide some background information about the energy systems the human body uses to produce energy in the form of adenosine tri phosphate (ATP: the direct fuel source for muscle contraction) and how these energy systems relate to blood lactate and LT testing. There are two main energy sources by which the body uses carbohydrates to provide ATP: 1) fast glycolysis and 2) slow glycolysis. There are other energy systems to produce energy: phosphagen, oxidative phosphorylation of fatty acids and protein. However, I will focus specifically on the energy systems that relate to lactic acid/lactate. What is important to note is both glycolytic pathways are almost always being utilized; however the contribution of each energy system is both time and intensity dependent.
At high intensities and/or short duration intervals fast glycolysis is used to provide the greatest percentage of ATP used for muscle contraction. The duration of work for fast glycolysis is between 30 seconds and 2 minutes. This system is very efficient at providing fast energy, which is needed given that the exercise duration is relatively short and the intensity is high. However, there are two important aspects of fast glycolysis: 1) the total energy provided in terms of ATP is low compared to systems that use oxygen (e.g. slow glycolysis) and 2) the by-product of fast glycolysis is lactic acid. Now there is a debate as to whether lactic acid leads to decreased pH (increased acidity), which inhibits muscle contraction (please see reference 1 for review). What is known is that lactic acid is immediately converted to blood lactate (which is what I measure during lactate threshold tests) and lactate can be used for some energy production via the Cori cycle (for review please see reference 2). However, one cannot use the fast glycolysis system to provide energy for long duration exercise. The importance of using lactate for measurement lies in that it is a marker that energy is being produced anaerobically (without oxygen) for muscles.
At lower intensities and/or longer duration exercise, the slow glycolysis system is increasingly relied upon to provide energy. The slow glycolysis system also uses carbohydrates for fuel; however, the benefit is more ATP is being produced for energy compared to fast glycolysis. The drawback is this energy system is slower, thus the intensity must be decreased. The duration of exercise where the contributions of fast glycolysis to slow glycolysis appear to transition is around 2-3 minutes of work.
To summarize:
1. Fast Glycolysis
a. Short-term, high intensity exercise
b. By product is lactic acid, which is immediately converted to lactate
e. Example is 400-meter dash
2. Slow glycolysis
a. Longer term, lower intensity
b. Example is 10 km run
How does this relate to lactate threshold testing?
In the past the term anaerobic threshold was widely used to describe the transition in exercise intensity where the body transitions from aerobic means of energy production (slow glycolysis) to anaerobic means of energy production (fast glycolysis). What is now known is the transition from aerobic to anaerobic energy is just that, a transition, and is based on length and intensity of exercise. There is not a clear breaking point where the body shifts from producing ATP exclusively using oxygen to producing ATP exclusively without oxygen. For example, a 4-minute all-out swim is 60% aerobic and 40% anaerobic, whereas a 3-minute all-out swim test is 50 % aerobic and 50% anaerobic (due to maintaining a higher intensity of work). The body does not go from 100% aerobic to 100% anaerobic at a breaking point (i.e. anaerobic threshold).
What is known is that as you increase your exercise intensity, the contributions of anaerobic energy systems (ie. fast glycolysis) increases and levels of blood lactate increase. As exercise intensity continues to increase, the contribution of the fast glycolysis energy system continues to increase leading to increased blood lactate production. A tipping point will finally occur with increasing exercise intensity where lactate production exceeds the removal of blood lactate and this is the lactate threshold (3). Lactate threshold has replaced the term of anaerobic threshold. Even though an athlete crosses the lactate threshold, oxidative means of energy production are still being used to supply the body with energy.
There are three determinants of endurance performance: VO2max, lactate threshold, and efficiency (4). It is important to note that these variables are inter-related. However, lactate threshold has repeatedly been shown to be predictive of endurance performance. Bishop, et al. (5) found lactate threshold was strongly related to 1 hr time trial performance in trained cyclists. Bentley, et al. (6) found that an earlier point of lactate threshold, known as Dmax correlates with 90 minute maximum power output. Furthermore, Dumke et al. (7) found that heart rate at three definitions of lactate threshold (Dmax, lactate deflection point, and OBLA) significantly correlate with heart rate during a 60-minute cycling time trial. The 4-mmol lactate threshold level is called onset of blood lactate accumulation (OBLA). One can use this lactate threshold level (OBLA) to design training zones (8, 9, 10). By designing a training zone with the top of the zone just below or slightly above lactate threshold (i.e. zone 4), one can then have a zone to develop specific workouts to improve lactate threshold performance (based on the exercise physiology principle of specificity), and thus improve overall endurance performance.
While lactate threshold testing is valuable for designing training zones and monitoring training progress, there is another point of intensity that can be monitored using blood lactate levels. This is the exercise intensity at which blood lactate levels remain stable and is the maximum lactate steady state (MLSS). This intensity reflects a balance between lactate production and removal (11). The importance of MLSS is that it defines a point of exercise intensity where muscles use negligible anaerobic energy systems for energy (12) and marks the boundary between the heavy exercise domain and severe exercise domain (13). Historically, testing for MLSS has required multiple laboratory visits where each visit included a 30-minute trial at a set exercise intensity and blood lactate is repeatedly measured to evaluate for any increased lactate levels (12, 14, 15). A decade ago, Swensen, et al (16) found that a simulated cycling 5K-time trial could be used to predict the maximum lactate steady state. This protocol was then cross-validated by Harnish, et al. (15). I have been using this protocol for several years to non-invasively determine MLSS in my athletes to 1) track training progress and 2) set the training zone for long tempo rides, especially for my Ironman athletes. Furthermore, I have been collecting some pilot data that has shown a relationship between the MLSS heart rate and Ironman bike leg heart rate. To date there have not been any published studies that have shown this relationship. At this time, I do not currently propose athletes ride the Ironman bike leg at MLSS (unless I am coaching the specific athlete full time and we have determined this intensity is manageable for long-course training brick sessions).
1. Robergs RA, Ghiasvand F, Parker D. Biochemistry of exercise-induced metabolic acidosis. Am J Physiol Regul Integr Comp Physiol. 2004;287(3):R502-16.
2. Gladden LB. A lactatic perspective on metabolism. Med Sci Sports Exerc. 2008;40(3):477-85.
3. Powers SK, Howley, ET. Exercise Physiology: Theory and Application to Fitness and Performance.5th ed. New York (NY): McGraw-Hill; 2004. 57p.
4. Joyner MJ, Coyle EF. Endurance exercise performance: the physiology of champions. J. Physiol. 2008;586(1):35-44.
5. Bishop D, Jenkins DG, Mackinnon LT. The relationship between plasma lactate parameters, Wpeak and 1-h cycling performance in women. Med Sci Sports Exerc. 1998;30(8):1270-5.
6. Bentley DJ, McNaughton LR, Thompson D, Vleck VE, Batterham AM. Peak power output, the lactate threshold, and time trial performance in cyclists. Med Sci Sports Exerc. 2001;33(12):2077-81.
7. Dumke CL, Brock DW, Helms BH, Haff GG. Heart rate at lactate threshold and cycling time trials. J Strength Cond Res. 2006;20(3):601-7.
8. Esteve-Lanao J, Foster C, Seiler S, Lucia A. Impact of training intensity distribution on performance in endurance athletes. J Strength Cond Res. 2007;21(3):943-9.
9. Faria EW, Parker DL, Faria IE. The science of cycling: physiology and training - part 1. Sports Med. 2005;35(4):285-312.
10. Friel J. The Triathlete's Training Bible. 3rd ed. Boulder (Co): Velo press; 2009. 46 p.
11. Heck H, Mader A, Hess G. Justification of the 4 mmol/l lactate threshold. Int J Sports Med 1985;6(3): 117-30.
12. Antonutto G, Di Prampero PE. The concept of lactate threshold. A short review. J Sports Med Phys Fitness. 1995;35(1):6-12.
13. Pringle JS, Jones AM. Maximal lactate steady state, critical power and EMG during cycling. Eur J Appl Physiol. 2002;88(3):214-26.
14. Beneke R, von Duvillard SP. Determination of maximal lactate steady state response in selected sports events. Med Sci Sports Exerc. 1996;28(2):241-6.
15. Harnish CR, Swensen TC, Pate RR. Methods for estimating the maximal lactate steady state in trained cyclists. Med Sci Sports Exerc. 2001;33(6):1052-5.
16. Swensen TC, Harnish CR, Beitman L, Keller BA. Noninvasive estimation of the maximal lactate steady state in trained cyclists. Med Sci Sports Exerc. 1999;31(5):742-6.
