Lactate in Running: Understanding Its Role, Thresholds, and Training Implications

What Does Lactate Mean in Running?

In running, lactate is a crucial byproduct of anaerobic energy production that, contrary to popular belief, serves as a vital fuel source and signaling molecule, rather than merely a waste product causing fatigue. Understanding lactate is key to optimizing training and performance by identifying an individual's lactate threshold, which dictates the highest intensity that can be sustained aerobically.

Understanding Energy Production for Runners

To sustain any physical activity, including running, our bodies require adenosine triphosphate (ATP), the primary energy currency of cells. ATP is produced through several interconnected energy systems:

• Aerobic System: Utilizes oxygen to efficiently break down carbohydrates and fats, producing large amounts of ATP for sustained, lower-intensity efforts.
• Anaerobic Systems: Produce ATP without oxygen. These include the phosphagen system (for very short, explosive bursts) and glycolysis (for high-intensity efforts lasting from seconds to a few minutes).

During high-intensity running, when oxygen supply cannot meet the demand for ATP production, the body increasingly relies on anaerobic glycolysis. This is where lactate comes into play.

What Exactly is Lactate? Dispelling the "Lactic Acid" Myth

For decades, "lactic acid" was blamed for muscle fatigue and soreness. However, modern exercise science clarifies that the molecule produced is lactate, not lactic acid, under normal physiological conditions.

• Formation: When glucose is broken down via glycolysis, pyruvate is formed. If oxygen is abundant, pyruvate enters the mitochondria for further aerobic energy production. However, during intense exercise, when oxygen supply is limited relative to demand, pyruvate is converted to lactate. This conversion is vital because it regenerates NAD+, a coenzyme essential for glycolysis to continue producing ATP.
• pH Neutrality: The term "lactic acid" implies an acidic compound. While lactic acid can be formed, it rapidly dissociates into lactate and a hydrogen ion (H+) at the body's normal pH. It's the accumulation of these hydrogen ions (not lactate itself) that can contribute to a decrease in muscle pH, potentially interfering with muscle contraction and contributing to a sensation of fatigue. Lactate itself is a neutral salt.

Lactate as a Fuel Source: The Lactate Shuttle

Far from being a mere waste product, lactate is a highly versatile molecule that plays a significant role in energy metabolism:

• Fuel for Other Tissues: Lactate can be transported out of the muscle cells where it's produced and shuttled to other tissues, such as slow-twitch muscle fibers, the heart, and the brain, where it's converted back to pyruvate and used as an efficient fuel source aerobically.
• Cori Cycle: Lactate can also travel to the liver, where it's converted back into glucose through a process called the Cori Cycle (gluconeogenesis). This newly formed glucose can then be released back into the bloodstream to fuel working muscles, especially during prolonged exercise or recovery.
• Signaling Molecule: Emerging research suggests lactate acts as a signaling molecule, influencing gene expression and adaptation to exercise.

Lactate Threshold: A Critical Performance Indicator

For runners, the concept of lactate threshold (LT) is paramount. It represents the intensity of exercise at which lactate begins to accumulate in the blood at a rate faster than it can be cleared.

• Measurement: Lactate threshold is typically determined in a laboratory setting through a graded exercise test, where blood samples are taken at increasing intensities to measure blood lactate concentrations.
• Significance: A higher lactate threshold means an athlete can sustain a faster pace or higher power output for a longer period without experiencing significant fatigue due to lactate accumulation. It's a stronger predictor of endurance performance than V̇O2 max (maximal oxygen uptake) for well-trained athletes, as it reflects the ability to utilize a high percentage of V̇O2 max efficiently.

From Lactate Threshold to Onset of Blood Lactate Accumulation (OBLA)

Distinctions are often made between different "thresholds" related to lactate:

• First Lactate Threshold (LT1) / Aerobic Threshold: This is the point at which blood lactate levels begin to rise slightly above baseline, indicating a shift from predominantly fat metabolism to increased carbohydrate utilization. It signifies the upper limit of truly aerobic exercise where lactate production and clearance are perfectly balanced.
• Second Lactate Threshold (LT2) / Onset of Blood Lactate Accumulation (OBLA) / Anaerobic Threshold: This is the critical point where blood lactate accumulates rapidly and exponentially. At or above OBLA, the body cannot clear lactate as quickly as it's produced, leading to a steady rise in lactate levels, increased hydrogen ion accumulation, and eventual fatigue. This intensity can typically only be sustained for a limited duration (e.g., 20-60 minutes for trained athletes).

Training to Improve Your Lactate Threshold

Improving your lactate threshold is a cornerstone of endurance running training. It allows you to run faster for longer. Key training methods include:

• Tempo Runs: These involve sustained efforts (e.g., 20-60 minutes) at an intensity just below, at, or slightly above your lactate threshold. The goal is to accustom the body to clearing lactate efficiently while running at a challenging but sustainable pace.
• Interval Training: Shorter, higher-intensity efforts (e.g., 3-10 minutes) at or above your lactate threshold, interspersed with recovery periods. This type of training pushes the body to produce and clear lactate at higher rates, improving both lactate production capacity and clearance mechanisms.
• Long Runs: While primarily focused on building aerobic base, consistent long runs at an easy-to-moderate pace improve mitochondrial density and capillary networks, which indirectly enhance the body's ability to utilize oxygen and clear lactate more effectively.

Debunking the "Lactic Acid Causes Soreness" Myth

It's important to reiterate that lactate does not cause the delayed onset muscle soreness (DOMS) experienced a day or two after intense exercise. Lactate is rapidly cleared from the bloodstream within minutes to an hour after exercise. DOMS is primarily attributed to microscopic damage to muscle fibers and the subsequent inflammatory response.

Practical Takeaways for Runners

• Lactate is a Fuel, Not a Foe: Embrace lactate as a vital component of your energy system. It's an indicator of intensity and a temporary fuel source.
• Threshold is Key: Your lactate threshold is a powerful metric for guiding your training and predicting performance. Aim to increase the speed you can sustain at your lactate threshold.
• Train Smart: Incorporate a variety of training intensities, including tempo runs and intervals, to specifically target and improve your lactate handling capabilities.
• Listen to Your Body: While scientific metrics are valuable, understanding your perceived exertion during different types of runs can help you gauge your effort relative to your thresholds.