Assessing the Lactate Threshold

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Assessing the Lactate Threshold
Trevor L. Gilllum, M.S. and Len Kravitz, Ph.D.

Article Reviewed
McGehee, J.C., Tanner, C.J., and Hourmar, J.A. (2005). A comparison of methods for estimating the lactate threshold. Journal of Strength and Conditioning Research, 19(3), 553-558.

Introduction
Lactate threshold (LT), defined as the exercise intensity at which blood lactate concentrations rise exponentially, has been identified in research as the best predictor of endurance performance (McGehee, Tanner and Hourmar, 2005). Though its importance in designing optimal endurance training programs has always been recognized, it has been difficult for recreational enthusiasts to ascertain their actual lactate threshold outside of a laboratory. This is because a lactate threshold laboratory test involves blood to be drawn at incremental stages of a progressively increasing exercise work bout, which is then analyzed for the appearance of lactate. Since the LT is the best predictor of running performance, it would be a wonderful assessment for personal trainers and fitness professionals to utilize with many of their clients. However, until recently, field methods to assess LT have not been well documented. This article will introduce and describe a research-tested field method that can accurately pin point a person's LT.

Brief Review: What is Lactate and Why Do We Care About its Threshold?
Lactate is merely a metabolic bi-product that is produced during the breakdown of carbohydrates. For over 80 years lactate has been described with a negative connotation, assuming that lactate produced lactic acid in the body that in turn made muscles 'burn' and running paces plummet. This premise has been shown to be incorrect (Robergs, Ghiasvand and Parker, 2004; see article in IFJ Volume 2(6), 23-25, 2005 for a comprehensive discussion on current understandings about lactate). The real culprit to acidosis, or 'the burn' is the accumulation of H+ ions in the muscle contractile environment. It is now known that lactate actually buffers the acidity in the cells by accepting H+ ions within its biochemical structure that would otherwise impair exercise performance. Indeed if it were not for lactate buffering or neutralizing this acidic 'milieu' (surrounding) in the cell, we would only be able to exercise at lower intensity levels.

While it is known that the production of lactate is beneficial, measuring its formation during intense exercise provides tremendous insight into training and racing for endurance athletes in all modes of exercise. Although there are many contributing causes for fatigue, perhaps one of the most consequential is the build up of H+ ions in the muscle cells during rigorous exercise. Since it is well-established that lactate production is directly related to H+ ion appearance, and H+ ion appearance is related to exercise intensity, scientists and exercise physiology technicians can measure lactate and get an accurate depiction of what's going on in the cell.

The LT is the fastest a person can continuously run, cycle, swim or aerobically exercise in a steady state bout without fatiguing (for up to an hour depending on the fitness level of the individual). In essence, it is a person's 'Maximal Steady State' of continuous exercise. If LT is exceeded, fatigue will ensue much sooner. If for example, at a 7:00 min/mile pace the body needs more ATP for energy production (more than what is produced in the cells mitochondria {the cells ATP production factory}) to continue muscle contraction, water will be used to break down ATP outside of the mitochondria. From this reaction, H+ ions will rapidly appear. As H+ ions accumulate, the presence of lactate rises to buffer the acidity so the exercise can continue. If the 7:00 min/mile is maintained for a prolonged workout (30-60 minutes) there will be an exponential rise in lactate production. The lactate threshold is depicted in the laboratory as the point where lactate begins to rise exponentially during progressively increasing exercise.

Importantly, it should be clarified that exercise intensity above the LT can only be maintained for a few minutes. Therefore, in almost any race or maximal steady state workout it is imperative to stay below LT. However, if the pace at the LT can be increased through training, then the times for races will invariably decrease.

So lactate threshold training is essentially training the body's physiology to be more resilient in its production of lactate. In other words, a recreational athlete can run faster without working harder. The exercise enthusiast is producing less lactate, which in turn means H+ ions production has decreased for the same intensity. Thus, the client or student is running, cycling or swimming faster while working at the same level of intensity.

Furthermore, training at LT has been shown to induce advantageous physiological adaptations to increase endurance performance (Dalleck and Kravitz, 2003). Therefore, there is clear evidence to support incorporating training to increase LT, but without the use of a laboratory and its skilled technicians many exercisers are left only to guess at their LT. However, there is now mounting field evidence revealing practical ways to quantify LT that is just as good as going to an exercise physiology laboratory.

The Field Methods Study
McGehee, Tanner and Hourmar, (2005) compared four field methods to a laboratory assessment of LT to find the most accurate test. The first of the four field methods was the VDOT method, consisting of entering times for 400- 800-m time trials into a formula to assess the running speed at LT. The second method was the 3,200-m time trail in which athletes ran maximally on an outdoor track. Times were entered into a regression equation designed to predict running speed at LT. The third method was a 30-min time trail where subjects ran as fast as they could on a treadmill set at 1% grade. The average running velocity during the 30-min was used as the running speed at LT. The fourth and final method was the Conconi test (Conconi et al.,1996) that asked athletes to increase running velocity uniformly every min by an increment that increased heart rate (HR) by no more than 8 beats/min until exhaustion. The HR during the last 10-sec of each min was used to calculate the average HR per min at the recorded running speed. The HR and running speed that matched the HR deflection point was used to identify the LT.

Results from this study demonstrate that both VDOT and the 30-min time trial methods were just as accurate in assessing running speed at LT as the assessment in the laboratory. Additionally, the 30-min time trial method demonstrated that HR at the LT could be accurately and easily obtained.

Field Test For Personal Trainers to Use with Interested Clients
Due to the simplicity and precision of the test, and the ability to obtain a heart rate and running speed (for running clients), the 30-min time trial method can be readily completed on an indoor treadmill for LT assessment. Initially have the client do a 5- to 10-minute low intensity warm-up. Then, have the client run (or speed walk) as fast he/she can for 30 minutes at a 1% grade. The average running speed is deemed the LT, while the average HR (collected every 5 minutes) over the 30-min test is the HR at LT. By collecting the HR at this LT pace, the fitness professional can also utilize this physiological data to train the client 1) at the LT, 2) just below the LT, and sometimes 3) just above the LT on all modes of cardiovascular exercise. Once HR or speed at the LT is known, the personal trainer and fitness professional can further design ultramodern LT training program for clients (see Dalleck and Kravitz, 2003 for more on designing training programs to improve the LT). What's more, the personal trainer now has a user-friendly and very accurate LT test to repeatedly assess clients every 3 to 6 months to determine the proficiency of the clients' training program.

Additional References:
Conconi F, Grazzi G, Casoni I, Guglielmini C, Borsetto C, Ballarin E, Mazzoni G, Patracchini M, and Manfredini F. (1996). The Conconi test: methodology after 12 years of application. International Journal of Sports Medicine, 17(7), 509-519.
Dalleck, L.C. & Kravitz, L. (2003). Optimize endurance training. IDEA Personal Trainer, 14(1) 36-42.
Robergs, R.A., Ghiasvand, F., & Parker, D. (2004). Biochemistry of exercise-induced metabolic acidosis. American J of Physiology: Regulatory, Integrative and Comparative Physiology. 287: R502-R516.

Bios:
Trevor L. Gillum is a Ph.D. student in exercise physiology at the University of New Mexico (Albuquerque). He is a triathlete with research interests in metabolism and ultra endurance exercise.

Len Kravitz, Ph.D., is the Program Coordinator of Exercise Science and Researcher at the University of New Mexico where he recently won the "Outstanding Teacher of the Year" award. Len was honored with the 1999 Canadian Fitness Professional “International Presenter of the Year” and the 2006 Canadian Fitness Professional “Specialty Presenter of the Year” awards and chosen as the American Council on Exercise 2006 "Fitness Educator of the Year”.