McGehee, J.C., Tanner, C.J., & Houmard, J.A. 2005. A comparison of methods for estimating the lactate threshold. Journal
of Strength and Conditioning Research,
19 (3), 553–58.
Lactate threshold (LT) is the point in exercise intensity at which blood lactate concentrations rise exponentially. LT has been identified in research as the best predictor of running or endurance performance (McGehee, Tanner & Houmard 2005). Though trainers have long recognized LT’s importance when designing optimal endurance training programs, it has been difficult to ascertain an endurance enthusiast’s actual lactate threshold outside of a laboratory. This is because the standard LT test, as performed in a lab, involves drawing blood at incremental stages of a progressively more intense exercise work bout, then analyzing the blood samples for the appearance of lactate.
Since LT is the best predictor of endurance performance, it would be a wonderful assessment for personal trainers (PFTs) and other fitness professionals to use with clients. Until recently, however, field methods for assessing LT have not been well documented. This article will introduce and describe a research-tested field method that can accurately pinpoint a person’s lactate threshold.
Training at the Lactate Threshold
Lactate is a metabolic byproduct produced during the breakdown of carbohydrates. For more than 80 years, lactate has been described with a negative connotation. The assumption has been that accumulation of lactate (or lactic acid) in the muscles and blood caused “the burn” (referred to as acidosis in science), leading to plummeting running and endurance performance results. This premise has been shown to be incorrect (Robergs, Ghiasvand & Parker 2004). See “Lactate—Not Guilty as Charged” by Len Kravitz, PhD, in the June 2005 issue of IDEA Fitness Journal for a comprehensive discussion on current understandings about lactate. The real culprit in acidosis is the accumulation of H+ ions (hydrogen ions, which are also referred to as protons) in the muscle’s contractile environment. It is now known that lactate actually buffers the acidity (burn) in the cells by accepting the accumulating H+ ions within its biochemical structure (Robergs, Ghiasvand & Parker 2004). Thus lactate helps to minimize any impairment to exercise performance due to acidosis. Indeed, if it were not for lactate’s role in buffering or neutralizing this acidic milieu in the cell, we would only be able to exercise at lower-intensity levels, because acidosis would dramatically inhibit muscle contraction.
Measuring the formation of lactate during intense exercise provides tremendous insight into the performance of endurance athletes in all modes of exercise. Although many causes contribute to fatigue, perhaps one of the most consequential is the buildup 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 muscle cell.
A person’s LT is the fastest he or she 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 the person’s “maximal steady state” of continuous exercise. If LT is exceeded, fatigue will ensue much sooner. Say, for example, that a client is running at a 7-minute-per-mile pace. If, to continue muscle contraction at this pace, the body needs more adenosine triphosphate (ATP) for energy production than the amount produced in the cell’s mitochondria (the cell’s ATP production factory), 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 will rise to buffer the acidity so the exercise can continue. If the 7-minute-per-mile pace is maintained for a prolonged workout (30–60 minutes), there will be an exponential rise in lactate production.
It should be clarified that exercise intensity above LT can be maintained for only 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 LT can be increased through training, then the times for races will invariably decrease.
Lactate threshold training is essentially training the body’s physiology to be more resilient in its production of lactate. In other words, the recreational or competitive endurance athlete can run faster without working harder. The athlete is producing less lactate, which in turn means the production of H+ ions 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.
As training at LT has been shown to induce advantageous physiological adaptations to increase endurance performance (Dalleck & Kravitz 2003), there is clear evidence to support incorporating training to increase LT. Moreover, with the ability to assess a client’s LT without necessitating a blood-draw, the practical implications for PFTs become apparent.
Out of the Lab and Onto the Field
McGehee, Tanner and Houmard (2005) compared four field methods to a laboratory assessment of LT to find the most accurate test, with 27 competitive distance runners and triathletes (24 males and three females with a minimum of 3 years’ competitive experience). The first of the four field methods was the VDOT (performance-based VO2max values based on time). VDOT consisted of entering race times for 400- and 800-meter time trials into a formula to assess the running speed at LT. The second method was a 3,200-meter time trial in which athletes ran maximally for that distance on an outdoor track. Times were then entered into a prediction (or regression) equation designed to predict running speed at LT. The third method was a 30-minute time trial in which subjects ran as fast as they could on a treadmill set at a 1% grade. The average running speed (or velocity) during the 30 minutes was used as the running speed at LT. The fourth method was the Conconi test (Conconi et al. 1996), which asked athletes to increase running velocity uniformly every minute by an increment that increased heart rate (HR) by no more than 8 beats per minute until exhaustion. The HR during the last 10 seconds of each minute was used to estimate an LT. Blood lactate was assessed every 3.5–4.0 minutes, with subjects performing a graded exercise test to exhaustion on a treadmill. Lactate was assessed using an automated blood lactate analyzer.
Results from this study demonstrated that both VDOT and the 30-minute time trial methods were just as accurate in assessing running speed at LT as the laboratory assessment. In addition, the 30-minute time trial method demonstrated that HR at LT could be accurately and easily obtained.
Implications for Personal Trainers
Owing to the simplicity and precision of the test, and the ability to obtain a heart rate and running speed (for a running client), the 30-minute time trial method can be readily completed on an indoor treadmill for LT assessment.
Initially have your client do a 5- to 10-minute low-intensity warm-up. Then have the client run (or speed-walk) as fast as possible for 30 minutes at a 1% grade. The average speed shown on the treadmill display is deemed the LT, while the average HR (collected every 5 minutes) over the 30-minute test is the HR at LT. Knowing the HR at LT, you can use this physiological data to train the client at LT, just below LT or sometimes just above LT on all modes of cardiovascular exercise.
Once you know a client’s HR or speed at LT, you can further design ultramodern LT training programs for the client (see Dalleck & Kravitz 2003, for more on designing training programs to improve LT). What’s more, you now have a user-friendly and very accurate LT test that you can repeat every 3–6 months, thereby determining the proficiency of the client’s training program.
The 30-minute time trial gives you a convenient LT field test to use with clients. You can also apply the information obtained from this practical test to track performance changes and develop more sophisticated training programs, whether for recreational or competitive endurance clients.
Trevor L. Gillum, MS, is a doctoral student in exercise physiology at the University of New Mexico at Albuquerque (UNMA). He is a triathlete with research interests in metabolism and ultra-endurance exercise.
Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at UNMA, where he recently won the Outstanding Teacher of the Year Award. In 2006 he
was honored as the Can-Fit-Pro Specialty Presenter of the Year and as the ACE Fitness Educator of the Year.
Conconi, F., et al. 1996. The Conconi test: Methodology after 12 years of application. International Journal of Sports Medicine, 17 (7), 509–19.
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 Journal of Physiology: Regulatory, Integrative and Comparative Physiology, 287 (3): R502–16.
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