Threshold Training for Triathlon: Lactate Threshold Guide

Threshold training in triathlon targets your lactate threshold—the intensity you can sustain for about an hour—through intervals at 95-105% of your threshold pace or power.

Raising your threshold is one of the most effective ways to get faster. A higher threshold means you can swim, bike, and run faster at the same relative effort.

What is Lactate Threshold?

The Science

Lactate threshold (LT) is the exercise intensity at which lactate begins to accumulate in the blood faster than it can be cleared.

Below threshold:

• Lactate is cleared efficiently
• Effort is sustainable
• Fat is a significant fuel source

Above threshold:

• Lactate accumulates
• Fatigue increases rapidly
• Glycogen becomes primary fuel
• Time to exhaustion decreases

Threshold in Racing

For Olympic and sprint distance, threshold fitness is crucial.

Determining Your Threshold

Swimming: CSS (Critical Swim Speed)

Test protocol:

1. 400m time trial (all-out)
2. Rest 10-15 minutes
3. 200m time trial (all-out)

Calculate CSS: CSS Calculator

Cycling: FTP (Functional Threshold Power)

Test protocol:

1. 20-minute all-out effort
2. Multiply average power by 0.95

Calculate FTP: FTP Calculator

Running: Threshold Pace

Test options:

1. 30-minute test: Run hard for 30 min, average pace ≈ threshold
2. Race-based: Recent 10K pace + 10-15 sec/km
3. Heart rate: 85-92% of max HR

Learn more: Triathlon Training Zones Explained

Threshold Workouts by Discipline

Swimming Threshold Sessions

CSS Intervals:

Warm-up: 300m easy, 4 x 50m drills
Main: 5 x 200m at CSS pace, 15s rest
      OR 3 x 400m at CSS pace, 20s rest
      OR 10 x 100m at CSS pace, 10s rest
Cool-down: 200m easy

Descending Set:

Warm-up: 300m
Main: 400m at CSS+5 sec/100m
      300m at CSS pace
      200m at CSS-3 sec/100m
      100m fast
      30s rest between each
Cool-down: 200m

Broken 1,500m:

Warm-up: 300m
Main: 5 x 300m at CSS pace, 10s rest
      (Simulates race without wall push-offs)
Cool-down: 200m

Cycling Threshold Sessions

Classic Threshold Intervals:

Warm-up: 15 min easy, include 3 x 30s builds
Main: 3 x 10 min at 100% FTP, 5 min easy
      OR 2 x 15 min at 95-100% FTP, 5 min easy
      OR 1 x 20-30 min at 95% FTP
Cool-down: 10 min easy

Over-Under Intervals:

Warm-up: 15 min
Main: 4 x (3 min at 105% FTP + 3 min at 90% FTP)
      No rest between over/under
      5 min easy between sets
Cool-down: 10 min

Sweet Spot (Sub-threshold):

Warm-up: 15 min
Main: 2 x 20 min at 88-93% FTP, 5 min easy
Cool-down: 10 min

Running Threshold Sessions

Tempo Run:

Warm-up: 15 min easy + strides
Main: 20-30 min continuous at threshold pace
Cool-down: 10 min easy

Cruise Intervals:

Warm-up: 15 min easy
Main: 4 x 8 min at threshold, 2 min jog
      OR 3 x 10 min at threshold, 3 min jog
Cool-down: 10 min easy

Threshold Ladder:

Warm-up: 15 min
Main: 5 min at threshold
      3 min easy
      8 min at threshold
      3 min easy
      10 min at threshold
      3 min easy
      5 min at threshold
Cool-down: 10 min

Programming Threshold Training

Frequency

Sample Build Phase Week

Progression Through Training

Early Build:

• Shorter intervals (5-8 min)
• More recovery
• Slightly below threshold

Late Build:

• Longer intervals (10-20 min)
• Less recovery
• At or slightly above threshold

Peak:

• Race simulation
• At race effort
• Full recovery between sessions

Read more: Triathlon Build Phase

Threshold Training Execution

How It Should Feel

At threshold:

• "Comfortably hard"
• Can speak in single words
• Controlled but labored breathing
• Sustainable for ~1 hour (but hard)
• RPE: 7-8/10

Pacing Strategy

For intervals:

• Start at target effort
• Don't go out too hard
• Maintain consistent effort
• Last interval shouldn't be slower

Common mistakes:

• Starting too fast (first interval fastest)
• Coasting between intervals
• Not hitting targets due to fatigue

Recovery Between Intervals

Monitoring Threshold Progress

Signs of Improvement

• Higher power/pace at same HR
• Lower HR at same power/pace
• Can sustain threshold longer
• Faster recovery between intervals

Testing Schedule

Retest threshold every 4-8 weeks:

• Swimming: 400m + 200m test for CSS
• Cycling: 20-minute FTP test
• Running: 30-minute threshold test

Adjusting Zones

When threshold improves:

• Recalculate all zones
• Update workout targets
• Don't wait until next test if clearly fitter

Common Threshold Mistakes

1. Too Much Threshold Training

Problem: Excessive Zone 4 work

Consequences:

• Accumulated fatigue
• Stagnation or regression
• Increased injury risk

Solution:

• Maximum 2-3 threshold sessions/week
• Balance with 80% easy training
• Include recovery weeks

2. Threshold Too Easy

Problem: Training at Zone 3 instead of Zone 4

Signs:

• Feels "moderate" not "hard"
• Could do more intervals
• Not reaching HR targets

Solution:

• Use power/pace, not just feel
• Push harder during work intervals
• Proper warm-up before intensity

3. Threshold Too Hard

Problem: Training above threshold

Signs:

• Can't complete intervals
• Significant pace drop-off
• Need excessive recovery

Solution:

• Start more conservatively
• Use accurate zones
• Don't race every interval

4. Inconsistent Effort

Problem: Variable pacing during intervals

Signs:

• First interval fastest
• Fade during long intervals
• "Yo-yo" pacing

Solution:

• Even pacing strategy
• Use metrics, not just feel
• Practice pacing discipline

Related Resources

• Triathlon Training Zones Explained - Zone overview
• Triathlon Build Phase - When to use threshold
• CSS Calculator - Find swim threshold
• FTP Calculator - Find bike threshold
• Lactate Threshold Glossary - Definition
• Triathlon Interval Workouts - More intensity sessions