Lactate Threshold Training: Complete Guide for Endurance Athletes

Introduction: The Most Trainable Performance Factor

In the world of endurance sports, lactate threshold (LT) stands as the single most predictive measure of performance for events lasting from 30 minutes to several hours. While VO2max gets more attention, it's largely genetically determined and responds minimally to training. Lactate threshold, by contrast, is highly trainable—athletes can improve their LT pace by 10-20% or more through proper training.

Your lactate threshold determines the fastest pace you can sustain without progressively accumulating fatigue. It's the intensity ceiling for marathon running, century cycling, and Ironman racing. Raise this ceiling, and you automatically become faster at everything from 10K runs to long training rides.

This guide will demystify lactate threshold—explaining the science, teaching you how to test it, and providing specific workouts to push it higher. Whether you're a runner, cyclist, or triathlete, understanding and training your LT is the key to unlocking your endurance potential.

The Science of Lactate

Lactate has been misunderstood for decades. Once vilified as a "waste product" causing muscle burn and fatigue, we now know lactate is actually a valuable fuel source and critical signaling molecule. Understanding lactate physiology is essential for effective training.

What Is Lactate?

Lactate is produced constantly by working muscles, even at rest. During exercise, carbohydrate (glucose and glycogen) is broken down through glycolysis, producing pyruvate. When oxygen is plentiful, pyruvate enters the mitochondria for aerobic energy production. When energy demand exceeds aerobic capacity, pyruvate is converted to lactate, allowing glycolysis to continue.

Lactate as Fuel

Far from being a waste product, lactate is shuttled through the bloodstream to other tissues—including the heart, brain, and resting muscles—where it's converted back to pyruvate and used for fuel. The liver also converts lactate back to glucose (gluconeogenesis), helping maintain blood sugar during exercise.

The Lactate Shuttle

The "lactate shuttle" describes this movement of lactate between producing and consuming tissues. Training improves both sides: enhanced lactate production capacity in fast-twitch fibers and improved lactate clearance/oxidation in slow-twitch fibers and other tissues. This is one reason why lactate threshold is so trainable.

What Causes "The Burn"?

The burning sensation during intense exercise isn't directly caused by lactate, but by hydrogen ions (H+) that accumulate alongside lactate production. These hydrogen ions lower muscle pH (acidosis), interfering with muscle contraction and enzyme function. Training improves buffering capacity and acid tolerance, allowing higher work rates before failure.

Key Lactate Threshold Concepts

The term "lactate threshold" is used broadly, but exercise physiologists actually distinguish between multiple inflection points. Understanding these concepts helps you train more precisely.

LT1: Aerobic Threshold

LT1, or the first lactate threshold, occurs at approximately 2.0 mmol/L blood lactate. This is the intensity where lactate first begins to rise above baseline. Training below LT1 is purely aerobic and can be sustained for many hours. LT1 typically corresponds to 60-75% of maximum heart rate and defines the upper limit of "Zone 2" training.

LT2: Anaerobic Threshold / MLSS

LT2, the second lactate threshold (also called anaerobic threshold or OBLA—onset of blood lactate accumulation), occurs at approximately 4.0 mmol/L. This represents the maximal lactate steady state (MLSS)—the highest intensity where lactate production and clearance remain balanced. Beyond LT2, lactate accumulates progressively until exhaustion.

Functional Threshold (FTP/FTPace)

Functional threshold—FTP for cyclists, FTPace for runners—represents the maximum power or pace sustainable for approximately one hour. This practical definition closely approximates LT2 and is more easily measured through field testing than lab-based lactate analysis.

Fractional Utilization

Lactate threshold is often expressed as a percentage of VO2max. Untrained individuals might reach LT2 at 50-60% of VO2max, while elite endurance athletes can sustain 80-90% of VO2max at threshold. This "fractional utilization" is a primary target of threshold training.

Testing Your Lactate Threshold

Accurate threshold assessment is essential for setting appropriate training zones. Both laboratory and field tests have their place, and understanding their strengths helps you choose the right approach.

Laboratory Lactate Testing

Gold-standard testing involves incremental exercise with blood lactate sampling at each stage. Typically performed on a treadmill or bike ergometer, intensity increases every 3-5 minutes while a small blood sample (from fingertip or earlobe) measures lactate concentration. This identifies both LT1 and LT2 precisely.

30-Minute Time Trial Test

The most practical field test is a 30-minute all-out effort. Your average pace (running) or power (cycling) closely approximates LT2/FTP. This test is easily repeatable and requires no special equipment beyond standard training tools.

Critical Power/Critical Speed Testing

Critical power (CP) and critical speed (CS) testing use multiple time trials (typically 3, 12, and 20 minutes) to mathematically model your power-duration relationship. This approach provides additional insights including W' (anaerobic capacity) but requires multiple maximal efforts.

Heart Rate at Threshold (LTHR)

Lactate threshold heart rate provides a convenient way to monitor intensity when pace or power aren't available. LTHR is typically 85-92% of maximum heart rate but varies significantly between individuals. Always use individually tested values rather than age-predicted formulas.

Testing Best Practices

• Rest completely for 2-3 days before testing
• Test in consistent conditions (weather, time of day, equipment)
• Avoid caffeine and heavy meals for 3+ hours before testing
• Choose a flat, consistent course for running tests
• Retest every 6-8 weeks during structured training

Setting Training Zones from Lactate Threshold

Once you've determined your lactate threshold pace/power and heart rate, you can establish training zones that target specific physiological adaptations. Zone systems vary, but here's a practical 5-zone model anchored to LT2.

Zone 2: The Foundation

Zone 2 training (below LT1) builds the aerobic foundation upon which all other fitness depends. It enhances mitochondrial density, improves fat oxidation, increases capillarization, and develops cardiac efficiency. Most training volume—60-80%—should occur in Zone 2.

Zone 3: Sweet Spot/Tempo

Zone 3 sits between LT1 and LT2, offering high training stimulus with manageable recovery demands. It's particularly valuable for time-limited athletes who can't accumulate sufficient Zone 2 volume. However, it shouldn't replace true Zone 2 or Zone 4 work entirely.

Zone 4: Threshold Development

Zone 4 directly targets LT2 improvement. Work at or slightly above threshold teaches your body to produce and clear lactate at higher rates. This zone is demanding—limit threshold work to 1-2 sessions per week with adequate recovery.

Lactate Threshold Workouts

Effective threshold training applies the right stimulus at the right dose. Here are proven workout formats for developing lactate threshold, applicable to both running and cycling with appropriate adjustments.

Classic Tempo Run/Ride

Threshold Intervals

Cruise Intervals

Progressive Long Run/Ride

Over-Under Intervals

Running-Specific Threshold Training

Running threshold training follows the same principles as general threshold work but requires attention to running-specific factors: impact forces, terrain, and race distance demands.

LT Pace Guidelines by Race Distance

Sample Running Threshold Week

• Monday: Rest or cross-training
• Tuesday: Threshold intervals (4 × 8 min @ LT pace, 3 min recovery)
• Wednesday: Easy run, Zone 2 (45-60 min)
• Thursday: Easy run with strides (45 min + 6 × 20 sec)
• Friday: Rest or easy cross-training
• Saturday: Long run with tempo finish (90 min total, final 20 min at tempo)
• Sunday: Easy run, Zone 2 (50-60 min)

Running Form at Threshold

Threshold pace should feel "comfortably hard"—you can speak in short phrases but wouldn't want to hold a conversation. Focus on relaxed shoulders, quick cadence (170-180+ steps/min), and efficient arm swing. If form breaks down, the pace is too aggressive.

Cycling-Specific Threshold Training

Cyclists benefit from power meters that provide precise, instant feedback at threshold intensity. Cycling allows longer sustained efforts than running due to reduced impact stress, enabling higher threshold training volumes.

FTP and Threshold Relationship

Functional Threshold Power (FTP) approximates the power sustainable for one hour and closely matches LT2. The standard FTP test is a 20-minute all-out effort with FTP calculated as 95% of average power. Zone 4 (threshold) spans 91-105% of FTP.

Indoor vs. Outdoor Threshold Training

Indoor trainers eliminate variables (wind, terrain, traffic) that disrupt threshold efforts. Most athletes can produce 5-15 watts more outdoors due to better cooling and motivation, but indoors offers more consistent, measurable stimulus. Use both based on weather and workout demands.

Sample Cycling Threshold Week

• Monday: Rest
• Tuesday: Threshold intervals (3 × 15 min @ 95-100% FTP, 5 min recovery)
• Wednesday: Endurance ride, Zone 2 (90 min)
• Thursday: Over-unders (3 × 12 min alternating 105%/90% FTP)
• Friday: Rest or recovery spin (30-45 min Zone 1)
• Saturday: Long ride with tempo blocks (3+ hours, 3 × 20 min tempo)
• Sunday: Endurance ride, Zone 2 (2 hours)

Racing at and Below Threshold

Understanding your threshold enables precise race pacing. Whether racing at, below, or above threshold depends on event duration—and executing the right strategy separates podium finishes from blowing up.

Event Duration and Threshold

Negative Split Strategy

Starting conservatively (2-5% below target pace/power) and finishing faster produces better results than positive splitting. This preserves glycogen, manages lactate accumulation, and leaves capacity for a strong finish. Many records are set with negative or even splits.

Managing Surges

In mass-start events, surges above threshold are inevitable. Each effort above LT2 accumulates lactate debt that takes 3-5+ minutes to clear. Choose carefully when to respond to attacks—burning matches early often leads to late-race implosion.

Common Threshold Training Mistakes

Threshold training is powerful but easy to misapply. These common mistakes limit progress or lead to overtraining.

Mistake 1: Too Much Threshold Work

More isn't better. Threshold work is demanding and requires significant recovery. Two quality threshold sessions per week is optimal for most athletes; three is usually excessive. Additional volume should come from Zone 2, not more intensity.

Mistake 2: Training in No Man's Land

"Junk miles" in Zone 3—too hard for recovery, too easy for significant adaptation—should be minimized. When you train hard, train hard (Zone 4-5). When you train easy, train truly easy (Zone 1-2). The middle ground provides the worst return on investment.

Mistake 3: Starting Intervals Too Fast

Beginning threshold intervals above target intensity leads to premature fatigue and inability to complete the workout properly. Start each interval slightly conservative and settle into target pace/power. The goal is consistent efforts, not front-loaded heroics.

Mistake 4: Ignoring Recovery

Adaptation happens during recovery, not during the workout. Sleep, nutrition, and easy days are essential components of threshold development. If you're not recovering between sessions, reduce training load—you'll make faster progress.

Mistake 5: Never Retesting

As your threshold improves, yesterday's challenging pace becomes today's Zone 3. Regular retesting (every 6-8 weeks) ensures training zones remain calibrated. Training at outdated zones means suboptimal stimulus.

Recommended Gear for Threshold Training

Quality monitoring equipment enables precise threshold training. Here are our top recommendations for running and cycling.