For endurance athletes, understanding the concepts of lactate threshold and anaerobic threshold is crucial for optimizing training and race performance. While these terms are often used interchangeably, they represent distinct physiological concepts that have significant implications for how you train and compete.
What Is Lactate Threshold?
Lactate threshold (LT) is the exercise intensity at which lactate begins to accumulate in the bloodstream faster than it can be cleared. Contrary to popular belief, lactate is always being produced during exercise, even at very low intensities. The threshold represents the point where production outpaces clearance.
At rest and during easy exercise, your body efficiently processes lactate as it's produced. As intensity increases, lactate production rises, but your body can still manage it effectively. However, once you cross your lactate threshold, lactate accumulates rapidly in the blood, leading to fatigue and forcing you to reduce intensity.
The Science Behind Lactate Threshold
Lactate is produced when your muscles break down carbohydrates for energy through glycolysis. When oxygen is readily available, pyruvate (the end product of glycolysis) enters the mitochondria for aerobic metabolism. When energy demands exceed what aerobic metabolism can provide, pyruvate is converted to lactate.
Importantly, lactate itself isn't the villain it was once thought to be. Modern exercise physiology recognizes lactate as a valuable fuel source that can be shuttled between cells and converted back into energy. The accumulation of lactate is more of a marker of metabolic stress than a cause of fatigue itself.
What Is Anaerobic Threshold?
Anaerobic threshold (AT) is classically defined as the exercise intensity at which anaerobic energy pathways begin to dominate over aerobic metabolism. This concept emerged from the idea that there's a distinct point where your body "switches" from primarily aerobic to primarily anaerobic energy production.
However, this definition is somewhat outdated. We now know that both aerobic and anaerobic metabolism occur simultaneously at all exercise intensities, it's the relative contribution of each that changes. The term "anaerobic threshold" has largely fallen out of favor in scientific literature, though it remains common in coaching and popular fitness contexts.
Are Lactate Threshold and Anaerobic Threshold the Same Thing?
Here's where it gets interesting: while lactate threshold and anaerobic threshold are often used interchangeably, they're not technically the same thing, though they occur at similar intensities for most athletes.
Lactate threshold is a measurable, specific point based on blood lactate concentrations. It can be precisely determined through lactate testing during a graded exercise test.
Anaerobic threshold is more of a conceptual framework referring to the point where anaerobic metabolism becomes more dominant. It's harder to measure directly and is often estimated based on lactate measurements or ventilatory markers.
In practice, coaches and athletes often use these terms to describe the same intensity zone, the highest sustainable pace you can maintain for extended periods (roughly 30-60 minutes at maximum effort). For practical training purposes, this distinction matters less than understanding where this intensity falls in your training zones.
Identifying Your Threshold: LT1 and LT2
Modern lactate testing has refined our understanding by identifying two distinct lactate thresholds:
Lactate Threshold 1 (LT1) - Aerobic Threshold
LT1 represents the first rise in lactate above baseline levels, typically occurring at around 2 mmol/L of blood lactate. This is your aerobic threshold, the upper limit of truly easy exercise. Below LT1, you can sustain effort almost indefinitely with proper fueling.
Lactate Threshold 2 (LT2) - Lactate Threshold
LT2 is where lactate accumulation accelerates rapidly, typically occurring at around 4 mmol/L. This is what most athletes refer to as "lactate threshold" or "anaerobic threshold" - the maximum sustainable intensity for efforts lasting 30-60 minutes.
Why These Thresholds Matter for Training
Understanding your lactate threshold (or anaerobic threshold) allows you to structure training more effectively:
Zone 2 Training (Below LT1)
Training below your aerobic threshold builds mitochondrial density, enhances fat oxidation, and develops the aerobic base essential for endurance performance. This is where you should spend the majority of your training volume.
Threshold Training (Around LT2)
Training at or near your lactate threshold improves your body's ability to clear lactate, increases the intensity you can sustain before lactate accumulates, and enhances your race-pace endurance. These sessions are metabolically demanding and require adequate recovery.
Above Threshold (VO2max and Anaerobic Work)
Training above threshold develops your maximum aerobic capacity and anaerobic power. These high-intensity sessions complement threshold and base training but should comprise a smaller portion of your overall training volume.
How to Determine Your Lactate Threshold
Several methods can help you identify your threshold:
Laboratory Lactate Testing
The gold standard involves a graded exercise test with blood lactate measurements at increasing intensities. While accurate, this requires specialized equipment and typically costs $150-300.
Field Tests
- FTP Test (Cycling): A 20-minute maximal effort, with threshold estimated at 95% of average power
- 30-Minute Time Trial: Directly measures threshold pace or power
- Talk Test: Your threshold typically falls where conversation becomes difficult but short phrases remain possible
Heart Rate and Perceived Exertion
Your threshold typically occurs at 85-90% of maximum heart rate, though this varies by individual. It should feel "comfortably hard" - sustainable, but requiring focused effort.
Training Your Lactate Threshold
Improving your threshold requires targeted training:
Threshold Intervals
Sustained efforts at 95-105% of threshold intensity, typically 2x20 minutes or 3x15 minutes with short recovery periods. These sessions directly challenge your lactate clearance capacity.
Sweet Spot Training
Efforts at 88-94% of threshold power or pace provide significant training stimulus with less fatigue than true threshold work, allowing for higher training volume.
Long Aerobic Rides/Runs
Extended sessions below LT1 improve the underlying aerobic system that supports threshold performance.
The Practical Reality for Athletes
While the scientific distinctions between lactate threshold and anaerobic threshold are interesting, the practical takeaway is simpler: there's an intensity range where your body transitions from sustainable aerobic effort to unsustainable high-intensity work. Training this intensity improves your ability to sustain harder efforts for longer.
Whether you call it lactate threshold, anaerobic threshold, or simply "threshold," the key is identifying this intensity for yourself and incorporating appropriate training to improve it. For most endurance athletes, threshold training should comprise 10-20% of weekly training volume, with the bulk of work remaining at easier aerobic intensities.
Understanding these concepts helps you train smarter, pace races more effectively, and make sense of the physiological adaptations that occur as you improve. Rather than getting caught up in terminology debates, focus on the practical application: train your threshold regularly but not excessively, build a strong aerobic base, and watch your sustainable race pace improve over time.
Key Takeaways
- Lactate threshold is the point where lactate accumulates faster than your body can clear it
- Anaerobic threshold is a related concept referring to the shift toward anaerobic metabolism
- In practice, these terms describe the same intensity zone - your maximum sustainable pace
- Two thresholds exist: LT1 (aerobic threshold) and LT2 (lactate threshold)
- Threshold training improves your ability to sustain higher intensities
- Most training should occur below threshold, with targeted threshold sessions comprising 10-20% of volume
- Testing your threshold helps personalize training zones and track improvement
By understanding these physiological markers and training them appropriately, you'll develop the endurance foundation necessary for breakthrough performances in your chosen sport.