The Truth About Lactate Threshold

Lactate threshold is often misunderstood. Lactate itself isn’t the cause of fatigue—it’s a fuel and surrogate marker for metabolic state. Modern training should focus on lactate clearance capacity and maximum lactate steady state (MLSS) rather than obsessing over arbitrary zone thresholds. Understanding lactate enables more effective threshold training.

The Misconception

Lactate gets blamed for fatigue. This came from early animal research where scientists noticed lactate increased alongside fatigue and assumed causation: “Rising lactate = fatigue building up.”

The reality (established for 40+ years): Lactate is a fuel source, not a toxin. It doesn’t cause fatigue.

What Lactate Actually Is

The Science

When muscles work aerobically, they produce pyruvate. Pyruvate can either:
1. Be used for energy in the aerobic system
2. Be converted to lactate for transport to other tissues

Lactate is then:
– Transported to other muscles that use it for fuel
– Sent to the liver to be reconverted to glucose (Cori cycle)
– Used directly by the heart which preferentially burns lactate

Lactate = fuel transport system, not fatigue cause.

Why We Measure It

Scientists measure lactate because it’s:
1. Easy to measure – Take a finger prick blood sample, use a lactate analyzer
2. Correlates with fatigue markers – Appears at similar times as hydrogen ions, acidosis, and other actual fatigue contributors

Key insight: Lactate is a surrogate marker—it correlates with the right intensity ranges, but doesn’t cause the fatigue. It’s the passenger, not the driver.

The Lactate Threshold Concept

Traditional Definition

The lactate threshold is the point where lactate production exceeds lactate clearance capacity. On a lactate curve, this appears as the inflection point where lactate begins rising rapidly rather than staying relatively stable.

In zone models (often criticized but useful for reference):
– LT1 (Lactate Threshold 1): Initial rise in lactate—boundary between aerobic and aerobic/anaerobic mixed
– LT2 (Lactate Threshold 2): Rapid rise in lactate—where metabolic acidosis becomes significant

Zone 3 (in 5-zone models) sits between LT1 and LT2.

The Problem with Lactate Curves

In real-world testing, lactate curves don’t always look clean:
– Sometimes the threshold is obvious
– Sometimes it’s ambiguous or doesn’t exist
– Different testing protocols produce different thresholds in the same athlete
– Research identifies 10+ different methods to calculate lactate threshold

If scientists can’t precisely define it, should we obsess over it? Probably not.

What Actually Matters: MLSS

Maximum Lactate Steady State (MLSS) is more useful than “lactate threshold”:

MLSS = the highest intensity an athlete can sustain where lactate production = lactate clearance. Above MLSS, lactate continues rising and fatigue accumulates. At or below MLSS, the athlete can theoretically continue indefinitely.

Practical application: This is roughly your Lactate Threshold Training pace—the intensity you can hold for 20-60 minutes.

Lactate Threshold Values: What’s Normal?

Demolishing the “4 mmol” Myth

Old dogma: “Lactate threshold occurs at 4 millimoles of lactate.”

Reality: Lactate threshold varies enormously:
– Can be as low as 2 mmol
– Can be as high as 6-8 mmol
– Depends on training status, genetics, and testing protocol

Well-trained endurance athletes typically have higher lactate thresholds (more lactate clearance capacity).

Training the Lactate Threshold

Types of Threshold Work

Threshold runs/workouts: Sustained efforts at approximately MLSS intensity
– Duration: 20-40 minutes in one effort, or broken into shorter intervals
– Intensity: “Comfortably hard”—sustainable but definitely working
– Frequency: 1-2x weekly during specific training phases

Examples:
– 1 × 20-30 minute threshold run
– 3-4 × 8-10 minute threshold intervals with 2-3 minute recovery
– 2-3 × 15 minute threshold efforts

How Threshold Training Works

Threshold work improves:
1. Lactate clearance capacity – Body gets better at clearing/using lactate
2. Aerobic power – Can sustain higher absolute power at aerobic threshold
3. Economy – More efficient at intensities below threshold
4. Mental toughness – Sustained “hard” efforts build resilience

When Threshold Training Matters

Critical for:
– 5K runners – Threshold pace is close to race pace
– 10K runners – Significant portion of race at/near threshold
– Marathon runners – Some work above easy, below VO2 max

Less critical for:
– 1500m/mile runners – More emphasis on speed and VO2 max work
– 800m runners – Speed endurance matters more than threshold

For XC/high school runners: Threshold work is useful but not the cornerstone. Building the Championship XC Season emphasizes volume, aerobic base, and VO2 max work more than threshold-specific training.

Zone Models: Useful or Overstated?

The Debate

Criticisms of zone training:
1. Zones are arbitrary (where exactly does zone 2 end and zone 3 begin?)
2. Individual variation is huge (one person’s Z2 is another’s Z3)
3. Heart rate varies with fitness, fatigue, temperature, caffeine
4. Can create obsession with precise intensities instead of effort feel

Defense of zones:
1. Provides simple framework for programming
2. Helps beginners understand pacing
3. Zones roughly correspond to physiological systems
4. Better than random efforts

The middle ground: Use zones as loose guides, but prioritize feel and effort. Can you talk? Are you breathing hard? Is this sustainable for the intended duration? These matter more than hitting exact zone numbers.

Practical Threshold Training for High School Runners

Integration Into Training Cycle

Base phase: Threshold work less common; focus on Zone 2 Training for High School Runners and building aerobic base

Build phase: 1-2x weekly threshold sessions
– Example: Tuesday: 20-minute threshold run (after warm-up)
– Example: Thursday: 4 × 5 min threshold with 2 min jog recovery

Competition phase: Reduce to once weekly or every 10 days
– Maintain threshold capacity without excessive fatigue
– Lower volume but maintain intensity

Taper: Minimal threshold work; focus on short, sharp efforts

Workout Examples

Beginner threshold session:
– 10 min easy warm-up
– 4 × 4-5 min at threshold pace with 2 min jog recovery
– 5 min easy cool-down

Intermediate:
– 15 min warm-up (include strides)
– 2-3 × 8 min threshold with 2-3 min recovery
– 10 min cool-down

Advanced:
– 15 min warm-up
– 1 × 20-30 min sustained threshold
– 10 min cool-down

How to Find Threshold Pace

For high school runners without lactate testing:
1. Effort feel: Comfortably hard; could sustain 20-40 minutes
2. Talk test: Can speak short sentences but not full conversations
3. Comparison: Slightly faster than 10K race pace; much slower than mile race pace
4. Estimated: 25-35 seconds slower than 5K race pace (very rough)

Better: Use recent race results
– 5K race pace = slightly faster than threshold
– 10K race pace = slightly slower than threshold
– Threshold = somewhere between these

Why This Matters: The Big Picture

Understanding lactate properly means:
1. Stop blaming lactate for fatigue (it’s not the villain)
2. Focus on lactate clearance through training adaptation
3. Use threshold work strategically for 5K-10K distances
4. Don’t obsess over zone numbers (use them as guides)
5. Recognize individual variation (zones won’t be exact)

The Bottom Line

Lactate ≠ fatigue – It’s a fuel and marker, not the enemy
Threshold is useful but fuzzy – Useful for training, but don’t obsess over exact thresholds
MLSS is the real target – Understand it as max sustainable intensity
Threshold training matters for 5K-10K but less for very short (800m) or very long (marathon) distances
Feel matters more than zone numbers – Trust your body’s feedback
Individual testing beats estimates – If possible, get lactate tested for personalized training zones

For most high school coaches and runners, the key is balancing threshold work with the stronger priorities: aerobic base building (Zone 2 Training for High School Runners), VO2 max work, and race-specific preparation.

Related topics: Zone 2 Training for High School Runners, VDOT Paces vs Heart Rate Zones, Lactate Threshold Training, Essential XC Workouts