Understanding Lactate Threshold: LT1 vs LT2 and Why It Matters for Endurance Training

When it comes to endurance training, one of the most powerful concepts is the lactate threshold (LT). This is the point during increasing exercise intensity where lactate (a by-product of metabolism) begins to accumulate in the blood faster than the body can clear it.

By understanding and using lactate thresholds in training, athletes can optimize their workouts, improve performance, and better target their aerobic and anaerobic adaptations.

What Are LT1 and LT2?

Modern sports physiology often divides the lactate threshold into two key points: LT1 (first lactate threshold) and LT2 (second lactate threshold).

• LT1, sometimes called the aerobic threshold, is the intensity at which blood lactate concentration starts to rise above resting levels, but production and clearance remain roughly in balance. Below this point, lactate is removed as quickly as it's made. Data

  
  

• LT2, also known as the anaerobic threshold or maximal lactate steady state (MLSS), is the intensity where lactate begins to accumulate rapidly — the body cannot clear it as fast as it’s produced. 

  
  

Training between LT1 and LT2 defines the “threshold zone.” When athletes train in this zone, they stimulate important adaptations without overrelying on purely anaerobic systems.

Why Do Threshold Training?

Threshold training offers several key benefits:

1. Improved Endurance Performance Conditioning at or slightly below LT2 helps athletes sustain faster paces for longer before fatigue sets in.

2. Efficiency Gains Training near the lactate threshold improves the body’s ability to clear lactate, so for the same high intensity, less lactate accumulates. This increases work efficiency and delays exhaustion.

3. Aerobic Adaptations Work around LT1 encourages recruitment of type I (slow-twitch) muscle fibers, boosts mitochondrial enzymes, and enhances aerobic capacity.

4. Long-Term Sustainability Because threshold workouts are intense but not maximal, they can often be performed more frequently than very high-intensity intervals, reducing the risk of overtraining.

How to Identify LT1 and LT2

There are a few ways to pinpoint your lactate thresholds:

• Lab Testing: In a lab, athletes perform incremental exercise (e.g., on a treadmill or cycle ergometer). Blood samples are taken at each stage to measure lactate concentration. LT1 and LT2 are identified based on where lactate begins to rise steadily, then more sharply.

• Field-based Estimation: Without lab access, athletes can approximate their threshold via high-effort time trials or guided tests that extrapolate threshold pace / heart rate.

• Alternate Methods: Some use heart rate variability (HRV) or ventilatory thresholds (VT1 / VT2) as indirect markers of lactate thresholds.

Applying Threshold Training in Practice

Once LT1 and LT2 are known, they can be used to guide training zones. Here’s how to apply them:

• LT1 Zone Training: Focus on long, steady aerobic efforts just below LT1 to build endurance.

• LT2 Zone Training: Use tempo runs, sustained intervals, or “cruise intervals” that hover around LT2 — the key is to push but remain controlled.

• Periodization: Integrate threshold training into your macro plan. Over time, as your threshold improves, the pace at LT1 and LT2 should shift, which means you’ll need retesting or re-evaluation.

Final Thoughts

• LT1 is where lactate first accumulates but is still controlled — a great intensity for building aerobic fitness.

• LT2 marks the higher intensity where lactate builds faster than you can clear it — important for increasing sustainable high-intensity performance.

• Training in the threshold zone (between LT1 and LT2) helps you push your endurance limits, improve efficiency, and make smarter training decisions.

  
  

By testing for these thresholds and structuring workouts around them, whether in a lab or via field-based estimation, athletes can train more precisely, reduce wasted effort, and make meaningful gains.

References

• Training4Endurance. “Lactate Threshold Training (Updated 2021): The Definitive Guide.” Training 4 Endurance

• Loughborough University. “Training Zones – Lactate Thresholds.” Loughborough University

• Serpentine Running and Triathlon Club. “The benefits of threshold training.” serpentine.org.uk

• Verywell Fit. “Lactate Threshold Training: What Is It, Why It Matters.” Verywell Fit

• RunningTrips.co.uk. “LT1 and LT2 Explained.” runningtrips.co.uk