Lactate Thresholds (LT1 & LT2)

What It Is

Lactate thresholds represent two key intensity points where the body shifts how it produces energy:

• LT1 (Aerobic Threshold):
  The point where lactate begins to rise above resting levels. Training here builds aerobic durability and metabolic efficiency.

• LT2 (Anaerobic Threshold / FTP):
  The highest intensity you can sustain before lactate accumulates rapidly. This threshold closely aligns with FTP and marks the transition to heavy, unsustainable work.

Together, LT1 and LT2 define your training intensity spectrum and strongly influence your ability to sustain power.

ELI5 Version

• LT1 = easy simmer. You’re warming up the engine.
• LT2 = boiling point. Go any hotter and things spill over.

Why It Matters

• LT1 sets your endurance foundation. A higher LT1 means you can go faster at an easy effort.
• LT2 predicts race performance. It’s tied directly to sustainable power output (FTP).
• Defines training intensity distribution for polarized, pyramidal, and threshold-heavy plans.
• Improves with consistent training, especially structured tempo, sweet spot, and threshold work.

Practical Use

• Train below LT1 (Zone 2) for aerobic development and metabolic efficiency.
• Use Tempo and Sweet Spot to raise LT1 and LT2 together.
• Use Threshold intervals (Zone 4) to specifically push LT2 higher.
• Combine LT1/LT2 with VO₂ Max and HRV for a complete performance picture.
• Many cyclists use FTP tests as a practical LT2 approximation.

Rate of perceived exertion, power zones, and heart rate zones are all tools we use to approximate what is happening in the body with respect to LT1 and LT2. At any given time both aerobic and anerobic energy systems are active. We want to dose time spent under LT1, between LT1 and LT2, and above LT2 such that we get the desired fitness gains. What changes as we move across these thresholds is just the balance of the energy system (what contribution it has on the energy we generate to create power). For simplicity, you shouldn't really care too much about these thresholds if you're following a well built plan as the plan will ensure you're spending the right amount of time training each threshold.