Half Ironman Run Training: Half Marathon Off the Bike

Running a half marathon off the bike in a 70.3 demands specific brick training, as the 21.1km run feels significantly harder than a standalone half marathon.

After 1.9km of swimming and 90km of cycling, you face 21.1km of running on tired legs. This guide covers how to prepare for that unique challenge.

Run Time Targets

Critical note: These are off-the-bike times, not fresh half marathon times. Expect 10-20% slower than your standalone PR.

Calculate your target: 70.3 Calculator

Why the 70.3 Run is Different

Physiological Challenges

Fresh vs Off-the-Bike Comparison

Read more: Running Off the Bike

Training Structure

Weekly Run Sessions

Session Types for 70.3

Key Workouts

1. Long Run

Purpose: Build running-specific endurance

Duration: 70-120 min (building)
Intensity: Zone 2 (conversational)
Terrain: Flat to gently rolling
Focus: Consistent pace, good form

Progression:

2. Brick Run (Essential!)

Purpose: Train legs to run after cycling

Bike: 2-3.5 hours at race effort
T2: Practice quick transition
Run: 30-50 min
     First 10 min: Easy, let legs adapt
     Next 15-30 min: Build to race pace
     Final 5-10 min: Hold race pace

Brick Run Progression:

Learn more: Brick Workouts for Triathlon

3. Tempo Run

Purpose: Build sustainable race pace

Warm-up: 15 min easy
Main: 30-45 min at half marathon pace
      (goal race pace, not fresh HM pace)
Cool-down: 10 min easy
Total: 55-70 min

4. Interval Session

Purpose: Maintain speed, improve running economy

Warm-up: 15 min easy + strides
Main: 5-6 x 1km at 10K pace, 90s jog recovery
      OR 4 x 1 mile at threshold, 2 min jog
Cool-down: 10 min easy
Total: 50-60 min

5. Progressive Long Run

Purpose: Practice race-day negative splitting

Total: 90-105 min
Structure:
  First 60 min: Zone 2 (easy)
  Next 20 min: Marathon pace
  Final 10-25 min: Half marathon pace

Building to Half Marathon Distance

Long Run Progression

Don't Overdo the Long Run

For 70.3, you don't need 21km training runs:

• Maximum long run: 100-120 min
• Risk of injury outweighs benefit
• Brick runs more specific than fresh long runs
• Quality over quantity

Race Day Run Strategy

The First 5km: Survival Mode

The hardest part of any 70.3 run is the beginning.

What happens:

• Legs feel like concrete
• HR elevated from bike
• Pace feels impossible
• Brain says "quit"

What to do:

• Start 30-45 sec/km slower than goal
• Short, quick strides
• Walk through first aid station
• Trust that legs will come around

The Middle 11km: Find Rhythm

km 5-10:

• Settle into sustainable rhythm
• Check pace, adjust as needed
• Take nutrition at aid stations
• Stay mentally present

km 10-16:

• You're halfway
• Assess: maintain or push?
• Pick off competitors gradually
• Stay positive

The Final 5km: Push or Survive

If feeling good:

• Increase effort gradually
• Negative split the second half
• Strong finish to the line

If struggling:

• Walk/run is OK
• Every aid station
• One km at a time
• You WILL finish

Pacing Strategy

Conservative Approach (Recommended)

Example for 2:00 Goal (5:40/km average)

Read more: Triathlon Run Pacing

Nutrition During the Run

Fueling Targets

For 21.1km run (1:35-3:00):

• Carbs: 30-60g per hour
• Fluids: At every aid station
• Electrolytes: If hot

Aid Station Strategy

What to Consume

Common Run Mistakes

1. Starting Too Fast

The mistake: Trying to hit goal pace immediately The result: Blow up by km 10 The fix: First 5km should feel too slow

2. Not Enough Brick Training

The mistake: Only running fresh The result: Shocked by how hard race feels The fix: Weekly brick runs in build phase

3. Ignoring Nutrition

The mistake: Skipping aid stations The result: Bonking late in run The fix: Eat/drink at every station

4. Racing Others

The mistake: Chasing people who pass you early The result: Burning matches you'll need later The fix: Run YOUR race, pass them later

5. Mental Collapse

The mistake: Negative self-talk when it hurts The result: Walking more than necessary The fix: Prepare mantras, expect the pain

Sample 16-Week Run Build

Related Resources

• 70.3 Calculator - Race time prediction
• Half Marathon Pace Calculator - Pace targets
• Running Off the Bike - Why it feels hard
• Brick Workouts for Triathlon - Bike-to-run training
• 16-Week Half Ironman Plan - Complete program