Triathlon Build Phase: Race-Specific Intensity Guide

The triathlon build phase introduces race-specific intensity through threshold intervals, tempo work, and longer brick sessions while maintaining the aerobic base you've developed.

After building your aerobic foundation, the build phase transforms that engine into race-ready fitness. This is where training gets harder—and more specific to race demands.

Build Phase Purpose

What You're Developing

Intensity Shift

Build Phase Structure

Duration and Timing

• Duration: 4-8 weeks
• When: After 4-6 week base phase
• Before: 2-3 weeks peak/taper

Weekly Structure

Key Workouts

Threshold Intervals

Purpose: Raise lactate threshold, improve sustainable power/pace

Swim Threshold:

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

Use our CSS Calculator to find your threshold pace.

Bike Threshold:

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

Calculate your FTP: FTP Calculator

Run Threshold:

Warm-up: 15 min easy + 4 x 100m strides
Main: 3 x 10 min at threshold, 3 min jog
      OR 20-25 min continuous at threshold
Cool-down: 10 min easy

Learn more: Threshold Training for Triathlon

Tempo Sessions

Purpose: Build sustainable race-pace fitness

Swim Tempo:

Warm-up: 300m easy
Main: 1,200-1,500m at race effort
      (Slightly slower than threshold)
Cool-down: 200m easy

Bike Tempo (Sweet Spot):

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

Run Tempo:

Warm-up: 10 min easy
Main: 25-30 min at tempo (comfortably hard)
Cool-down: 10 min easy

Read more: Triathlon Tempo Workouts

Brick Workouts

Purpose: Train the bike-to-run transition

Build Phase Brick Progression:

Key Points:

• Bike at race effort (not race pace)
• Quick T2 transition
• Start run easy, build to race pace
• Last km at goal race pace

Essential reading: Brick Workouts for Triathlon

Interval Sessions

Purpose: Improve VO2max, speed, running economy

Swim Intervals:

Warm-up: 300m
Main: 8 x 100m at fast (but not sprint), 20s rest
      OR 4 x 200m at hard effort, 30s rest
Cool-down: 200m

Bike Intervals:

Warm-up: 15 min
Main: 5 x 5 min at 105-110% FTP, 3 min easy
      OR 4 x 8 min at 100-105% FTP, 4 min easy
Cool-down: 10 min

Run Intervals:

Warm-up: 15 min + strides
Main: 5 x 1km at 10K pace, 90s jog
      OR 6 x 800m at 5K pace, 2 min jog
Cool-down: 10 min

Learn more: Triathlon Interval Workouts

Sample Build Phase Weeks

Week 2 of 6 (10 hours)

Week 5 of 6 (11 hours)

Periodization Within Build Phase

3-Week Cycle

Most effective build phase structure:

Week 1: Moderate load, introduce intensity Week 2: Higher load, maintain intensity Week 3: Recovery (reduce volume 30-40%)

Then repeat for second 3-week cycle.

Volume Pattern

Week 1: ████████░░ (80% of peak)
Week 2: ██████████ (100% of peak)
Week 3: █████░░░░░ (60% - recovery)
Week 4: ████████░░ (80%)
Week 5: ██████████ (100%)
Week 6: █████░░░░░ (60% - recovery)

Maintaining Base Fitness

Don't Abandon Easy Training

Even in build phase:

• 75-80% of training stays easy
• Long sessions at Zone 2
• Easy sessions between quality days
• Active recovery important

The 80/20 Rule Still Applies

Monitoring Build Phase Progress

Signs of Positive Adaptation

• Threshold pace/power increasing
• Same hard efforts feel slightly easier
• Recovery between intervals improves
• Race simulation feels sustainable
• Energy levels remain good

Warning Signs (Too Much)

• Persistent fatigue
• Declining performance in intervals
• Elevated resting heart rate
• Poor sleep quality
• Loss of motivation
• Frequent illness

If warning signs appear: Take 3-5 easy days, reassess

Common Build Phase Mistakes

1. Too Much Intensity

Problem: Making every session hard

Solution:

• Maximum 3 quality sessions per week
• Keep easy sessions truly easy
• Honor rest days

2. Neglecting the Long Sessions

Problem: All intervals, no endurance

Solution:

• Maintain weekly long bike and run
• Long sessions at Zone 2
• Build aerobic endurance

3. Skipping Brick Workouts

Problem: Not prepared for race day

Solution:

• Weekly brick in build phase
• Practice race nutrition
• Progressive brick duration

4. Not Recovering

Problem: Accumulating fatigue

Solution:

• Recovery week every 3rd week
• Easy sessions between hard days
• Prioritize sleep

Transitioning to Peak/Taper

When to Move On

Ready for peak phase when:

• Completed 4-6 weeks of build
• Key workouts improving
• Race simulation successful
• 2-3 weeks until race

The Transition

Last build week → First taper week:

• Reduce volume 30-40%
• Maintain some intensity
• No new training stimulus
• Focus on freshness

Learn about tapering: Triathlon Taper Guide

Related Resources

• Triathlon Periodization Explained - Phase overview
• Triathlon Base Building - Previous phase
• Threshold Training for Triathlon - Intensity details
• Triathlon Interval Workouts - Speed work
• Brick Workouts for Triathlon - Bike-to-run training
• 12-Week Olympic Training Plan - Build phase in action