Leveraging Blood Lactate Response in Training, Part 1: LT1 and LT2 and Setting Training Zones

By Renee Eastman,
CTS Premier Coach & Performance Lab Director

Blood lactate plays a key role in exercise and fitness, offering valuable insights into how our bodies produce energy, build endurance, and perform. Often misunderstood as just a waste product, blood lactate is actually a powerful fuel source and an important messenger within the body. By understanding how lactate levels change during exercise, including the break points defined as LT1 and LT2, athletes can fine tune their training to boost performance and achieve higher fitness.

What is Blood Lactate?

Blood lactate is a byproduct of carbohydrate metabolism. It forms when glucose is broken down through glycolysis, producing pyruvate, which is converted into lactate by the enzyme lactate dehydrogenase. This process occurs under both aerobic and anaerobic conditions​.

Rather than being a mere waste product, lactate plays several vital roles in the body:

• Energy Source: Lactate is oxidized by muscles, the heart, and other tissues as a highly efficient fuel.
• Gluconeogenic Precursor: Gluconeogenesis is the process of producing glucose from non-carbohydrate sources, including lactate (from carbohydrate), glycerol (from fat), and amino acids (from protein).
• Signaling Molecule: Lactate acts as a “lactormone,” influencing metabolic pathways and cellular communication

A lactormone is lactate acting as a hormone-like signaling molecule. It helps regulate metabolism, coordinate energy use between cells, and trigger adaptations like mitochondrial growth, making it vital for optimizing the body’s response to exercise.

Why is Blood Lactate Important in Exercise?

During physical activity, blood lactate levels provide critical information about energy systems, performance thresholds, and training adaptations.

1. Indicator of Energy System Engagement

At lower exercise intensities, energy is primarily derived from aerobic metabolism, with minimal lactate production. As intensity increases, the anaerobic glycolytic system becomes more active, leading to a rise in lactate levels. This shift reflects the body’s transition from fat to carbohydrate as the dominant energy source.

2. Fuel Utilization During Exercise

Lactate is not just a byproduct but a critical fuel source. During prolonged activity, fast-twitch fibers produce lactate, which slow-twitch fibers and the heart consume. This “lactate shuttle” system redistributes energy across the body, supporting sustained performance.

3. Enhancing Recovery and Fatigue Management

Elevated lactate levels during or after exercise indicate anaerobic stress and highlight the body’s recovery needs. Efficient lactate clearance is a hallmark of good metabolic health and recovery capacity​.

4. Defining Key Thresholds for Training Zones

Blood lactate is integral in identifying two major performance thresholds:

• Lactate Threshold 1 (LT1): Also known as the aerobic threshold, LT1 marks the point where lactate levels first rise above resting levels. Training at or near LT1 enhances fat oxidation, aerobic efficiency, and overall endurance​. It is most closely associated with the top of Zone 2.
• Lactate Threshold 2 (LT2): The lactate threshold, sometimes referred to as anaerobic threshold, signifies the intensity where lactate accumulation surpasses clearance, resulting in fatigue. Training around LT2 improves the body’s ability to tolerate lactate, boosting high intensity performance​. This intensity is also closely associated with FTP (functional threshold power).

Lactate and Training Zones  

Setting and adhering training zones allows an athlete to individualize their training to better target specific energy system development and enhance training efficiency.  Lactate threshold (LT2) is the key physiological marker used to define training zones. Lactate Threshold varies between individuals and can be influenced by fitness level, training history, and genetics. Determining LT2 through testing (e.g., blood lactate, FTP tests, or critical power tests) allows for individualized training zones rather than relying on generic formulas based on a percentage of age-predicted maximum heart rate.

Laboratory Testing for Lactate Threshold, LT1 and LT2

Lab tests offer precise measurements of lactate levels, break points for LT1 and LT2, ventilatory responses, and heart rate at varying intensities. We perform these kinds of tests in our physiology lab in our Colorado Springs office. These tests are more precise and provide the most accurate results; however, they do require specialized equipment and trained personnel and come at a cost (usually $150-350 per test)

In an incremental exercise test an athlete performs a graded exercise test on a treadmill, bike, or ergometer, with intensity increasing in set intervals (e.g., every 3–5 minutes). During this test blood lactate is taken at the end of every stage to measure blood lactate concentration. In laboratory tests heart rate, perceived exertion, and often oxygen consumption (VO2) via a metabolic cart is also measured.

Identifying Thresholds:

• LT1: The point where blood lactate begins to rise above resting levels, often around 2 mmol/L, or the first noticeable inflection on the lactate curve​
• LT2: The intensity where lactate accumulates rapidly, exceeding the body’s clearance capacity, typically at 4 mmol/L or the second inflection on the curve.

Field Testing for Threshold

Field tests provide a practical alternative for athletes without access to lab facilities. While less precise, they can still effectively be used to set training zones because they use the training tools most athletes have access to with power meters, heart rate monitors, and GPS units.

• 8-Minute or 20-Minute Time Trial Test
  • The athlete performs an all-out 8-minute or 20-minute effort. Learn about differences between the 8- and 20-minute tests.
  • Average power or pace during this period is considered 110% (from 8-minute test) or 105% (from 20-minute test) of Lactate Threshold (LT2).
  • 90% of 8-minute average power output or 95% of 20-minute average power output is used as proxy for LT2 or FTP (functional threshold power)
  • 75% of estimated Lactate Threshold (LT2/ FTP) used to estimate Aerobic Threshold (LT1)

Setting Training Zones

Determining lactate threshold through testing (e.g., blood lactate, FTP tests, or critical power tests) allows for individualized training zones rather than relying on generic formulas. Laboratory testing is the gold standard for setting training zones because it uses an athlete’s specific physiology to set training zones based on blood lactate response. However, field tests are much more accessible to most athletes.  What’s most important is that athletes are taking the time to periodically and systematically evaluate threshold (power/ pace/ heart rate) to effectively structure their training. Here is a guide to when we’d recommend rechecking and updating your training zones.

References

Borszcz FK, Tramontin AF, Bossi AH, Carminatti LJ, Costa VP. Functional Threshold Power in Cyclists: Validity of the Concept and Physiological Responses. Int J Sports Med. 2018 Oct;39(10):737-742. doi: 10.1055/s-0044-101546. Epub 2018 May 25. PMID: 29801189.

Brooks GA. The Science and Translation of Lactate Shuttle Theory. Cell Metab. 2018 Apr 3;27(4):757-785. doi: 10.1016/j.cmet.2018.03.008. PMID: 29617642.

Cheng B, Kuipers H, Snyder AC, Keizer HA, Jeukendrup A, Hesselink M. A new approach for the determination of ventilatory and lactate thresholds. Int J Sports Med. 1992 Oct;13(7):518-22. doi: 10.1055/s-2007-1021309. PMID: 1459746.

Czuba, Miłosz, et al. “Lactate threshold (D-max method) and maximal lactate steady state in cyclists.” Journal of Human Kinetics 21.1 (2009): 49-56.

Author

Renee Eastman is a Premier coach for Carmichael Training Systems and has been with the company since 2001.  She has a bachelor’s degree and master’s degree in exercise physiology and is certified as a USA level 1 coach, NSCA Strength and Conditioning Specialist, and NASM Nutrition Coach.  She is a former competitive cyclist and a 6-time masters’ national champion.