Understanding LT1 and LT2: How Aerobic and Anaerobic Thresholds Shape Your Training

Quick Summary

• LT1 (aerobic threshold) marks the intensity where fat metabolism begins to give way to more carbohydrate use and is ideal for building endurance and mitochondrial fitness.
• LT2 (anaerobic or lactate threshold) is the intensity where lactate rises more quickly; improving it raises the fastest pace you can sustain for longer efforts.
• Use simple field markers—talk test for LT1, sustained time trials for LT2—or lab tests for precision; monitor heart rate, power, pace and perceived exertion.
• Training should include lots of volume below LT1, targeted sessions at/around LT2, and short high-intensity work above LT2 for speed and VO2max gains.

Introduction

If you train for endurance—running, cycling, rowing, or triathlon—you’ll see terms like LT1 and LT2, or aerobic and anaerobic threshold. Those thresholds are more than jargon: they describe physiologic tipping points that determine how you should structure mileage, intensity, and recovery. Knowing where your thresholds lie helps you train smarter, avoid burnout, and unlock better race performance.

What Are LT1 and LT2?

LT1 (Aerobic Threshold)

LT1 is often called the aerobic threshold. It’s the intensity at which your body starts to rely more heavily on carbohydrate energy compared with pure fat oxidation and when blood lactate begins to rise above baseline but remains low. Practically, LT1 corresponds to an easy-to-moderate effort you could sustain for hours and usually allows comfortable conversation.

LT2 (Anaerobic/Lactate Threshold)

LT2—also called the lactate threshold, anaerobic threshold, or onset of blood lactate accumulation (OBLA)—is a higher intensity where lactate production increases faster than your body can clear it. Work at or near LT2 feels “hard but steady” and is roughly the pace many trained athletes can hold for about an hour. Raising LT2 lets you sustain faster paces without fatiguing quickly.

The Physiology in Plain Language

Below LT1, your muscles primarily use oxygen and fat for fuel; mitochondria become more efficient, and endurance capacity grows. Between LT1 and LT2, carbohydrate use increases and lactate starts to accumulate but is still manageable. Above LT2, lactate and hydrogen ions accumulate rapidly, reducing muscle performance—this is where short, high-intensity efforts and repeated sprints are needed to improve tolerance and clearance.

How to Identify Your Thresholds

Field Methods (Practical and Cheap)

• Talk test: If you can easily hold a conversation, you’re below LT1. If you can speak short phrases but not hold a full conversation, you’re around LT2.
• 20–60 minute time trial: For an estimate of LT2, do a sustained maximal effort for 20–60 minutes—mean heart rate or power during the latter portion approximates LT2.
• Heart-rate drift and perceived exertion: Track where effort feels sustainable for long durations (LT1) and where it becomes taxing but steady (LT2).

Lab Tests (More Precise)

Laboratory lactate profiling or graded exercise tests with gas analysis can pinpoint LT1 and LT2 precisely by measuring blood lactate concentrations or ventilatory thresholds. These are ideal if you want exact numbers for heart rate and power zones.

Training Implications: What Each Threshold Tells You

Training Below LT1

Workouts below LT1 build aerobic base—fat-burning efficiency, capillary density, and mitochondrial function. Most coaches recommend a high volume of training in this zone, especially during base phases. Easy runs and long aerobic rides should live here. For guidance on pacing longer efforts, see tips on smarter long-run pacing.

Training At or Near LT2

Sessions at LT2 (tempo/threshold workouts) improve your ability to sustain high-intensity efforts and raise the pace you can hold for prolonged durations. Examples: 20–40 minute tempo runs, 2 x 20-min threshold intervals, or continuous efforts at a “comfortably hard” pace.

Training Above LT2

Intervals above LT2—shorter, high-intensity repeats—improve VO2max, neuromuscular power, and anaerobic capacity. These should be limited in volume and paired with ample recovery.

Sample Workouts

• LT1 session: 60–90 minutes easy aerobic run or ride—conversational pace, low effort.
• LT2 session: 3 x 15–20 minutes at threshold with 5–8 minutes easy jog between reps.
• Above LT2: 6–8 x 3 minutes hard with 3 minutes recovery, or short 30–60 second sprints for neuromuscular work.

Practical Steps and a Checklist

Use this step-by-step guide to find thresholds and build them into training.

1. Measure basics: know your resting heart rate, recent race times, and max HR estimates (see resources on resting heart rate).
2. Perform a field test: a 20–60 minute time trial to estimate LT2; use talk test sessions to mark LT1.
3. Create zones: map HR, pace, or power to your perceived effort zones—easy (below LT1), tempo (around LT2), and intervals (above LT2).
4. Program weekly: 70–80% volume below LT1, 10–20% targeted at/near LT2, and 5–10% high-intensity work, adjusted for your goals and fitness.
5. Include strength and recovery: add strength work 1–2x per week and prioritize recovery nutrition (see recovery fuel tips) and sleep.
6. Retest every 6–12 weeks and adjust zones as you improve.

Checklist

• Perform initial threshold test (20–60 min TT)
• Record heart rate/power/pace during tests
• Build weekly plan with majority volume below LT1
• Schedule 1 LT2 session and 1 high-intensity session per week (as appropriate)
• Strength session 1–2x weekly (see quick strength plan)
• Log recovery, sleep, and fueling

Common Mistakes

• Training too hard on “easy” days: this blunts aerobic gains and increases injury risk.
• Over-relying on heart rate without context: HR can drift with heat, fatigue, and dehydration—use RPE and pace/power too.
• Doing too much threshold work: chronic tempo overload is a fast track to stagnation and fatigue.
• Neglecting strength and recovery: strength training and proper fueling boost durability and threshold improvements.
• Testing too rarely: failing to retest means you might be training to outdated zones.

How This Affects Performance Potential

LT1 improvements make you more efficient at lower intensities, allowing longer, faster base-building sessions with less fatigue. Raising LT2 increases the speed you can sustain during races and hard efforts, shrinking the gap between you and faster competition. Ultimately, combining a broad aerobic base with targeted threshold and high-intensity work yields the best endurance improvements.

When to See a Coach or Get Lab Testing

If you’re training for a specific race, trying to break a personal record, or managing chronic fatigue/injuries, a coach or sport scientist can design precise tests and individualized plans. Lab testing can be worth the investment for competitive athletes who want accurate HR/power targets and detailed metabolic data.

Conclusion

LT1 and LT2 are practical tools for structuring effective endurance training. LT1 guides the majority of your easy-volume work and aerobic development; LT2 defines the intensity for sustained hard efforts and is a key determinant of race pace. Use simple tests, monitor multiple metrics, and balance volume, threshold work, and high-intensity intervals with strength and recovery to see steady gains. If something feels off or you have medical concerns, consult a healthcare professional or qualified coach.

Further Reading

• How resting heart rate relates to fitness
• Smarter long-run pacing and why easy runs matter
• Quick strength plan to support endurance training
• Recovery fueling strategies

FAQ

1. Q: How often should I test my thresholds?

   A: For most recreational athletes, retesting every 8–12 weeks is sufficient. Competitive athletes may test more frequently (every 4–6 weeks) to fine-tune training zones. Always interpret results alongside how you feel and recent training load.

2. Q: Can I use heart rate to find LT1 and LT2?

   A: Yes—heart rate is a useful proxy but can be influenced by fatigue, heat, hydration, and stress. Combine HR with perceived exertion, pace, or power for more reliable zones.

3. Q: Should I do most of my training below LT1?

   A: A large portion of your weekly volume should be low intensity (below LT1) to build aerobic capacity. The exact percentage depends on your goals, but many successful endurance programs emphasize a high proportion of easy work.

4. Q: Are tempo runs the same as training at LT2?

   A: Tempo runs typically target the area around LT2—sustained, comfortably hard efforts that improve your ability to clear and tolerate lactate. They’re an effective way to raise your threshold pace.

5. Q: Will strength training help my thresholds?

   A: Yes. Strength training improves muscle recruitment, running economy, and durability, which supports better performance at all intensities. Incorporate 1–2 weekly sessions like a short strength plan to complement endurance work.