Ironman Run Training: Marathon Off the Bike Guide

The Ironman marathon is unlike any standalone marathon—you'll run 42.2km on legs that have already swum 3.8km and cycled 180km, requiring specific brick training and pacing strategy.

Running a marathon at the end of an Ironman is where the race is won or lost. Thousands of athletes walk this marathon, but with proper training and pacing, you can run most of it—and finish strong.

Ironman Run Targets

Time Goals by Level

Reality check: Your Ironman marathon will be 15-30 minutes slower than your fresh marathon time.

Calculate your expected time: Ironman Time Calculator

The Unique Challenge

Why It's Different

Physiological Challenges

Leg fatigue:

• Cycling muscles partially overlap with running
• 5-6 hours of cycling creates significant damage
• Blood flow patterns need to shift

Metabolic depletion:

• Even with perfect nutrition, glycogen is reduced
• Fat oxidation becomes more important
• Pace must account for this

Neuromuscular fatigue:

• Brain-body connection is tired
• Form deteriorates more easily
• Concentration becomes harder

Learn more: Running Off the Bike

Weekly Training Structure

Volume Guidelines

Session Distribution

Key Training Sessions

1. Long Run (2-3 hours)

Purpose: Build marathon endurance and mental strength

Duration: 2:00-3:00

Structure Option A (Steady):
- Entire run at easy pace
- Heart rate Zone 2
- Practice run nutrition

Structure Option B (Marathon Finish):
- First 90 min: Easy pace
- Final 30-60 min: Marathon pace
- Teaches finishing strong

2. Brick Run (After Long Bike)

Purpose: Adapt to running on fatigued legs

After 4-6 hour bike:

Week 1-8:
  30-45 min run
  First 10 min very easy
  Rest at marathon pace if able

Week 9-16:
  45-60 min run
  First 5 min easy
  Build to marathon pace
  Include negative split

Week 17-22:
  60-90 min run
  First 5 min easy
  Rest at or faster than race pace

3. Tempo/Marathon Pace Run

Purpose: Race-specific fitness

Warm-up: 15 min easy

Main Set Options:

Option A (Tempo):
  40-50 min continuous at marathon pace
  
Option B (Intervals):
  4 x 10 min at marathon pace
  3 min easy jog between

Cool-down: 10 min easy

Total: 65-80 min

4. Easy Recovery Runs

Purpose: Build base, promote recovery

Duration: 35-50 min
Effort: Truly easy (Zone 1-2)
Pace: Conversational
Frequency: 2-3x per week

Key points:
- Should feel effortless
- Don't chase pace
- Recovery is the goal

Training Progression

Base Phase (Weeks 1-8)

Focus: Build consistent running volume

Brick Runs: 30-40 min after long bike

Build Phase (Weeks 9-16)

Focus: Extend long run, build brick run

Brick Runs: 45-60 min after long bike Tempo Work: Weekly marathon pace sessions

Peak Phase (Weeks 17-22)

Focus: Maximum long runs, race simulation bricks

Brick Runs: 60-90 min after 5+ hour bike Race Simulation: Full bike + 75-90 min run

Taper Phase (Weeks 23-24)

Brick Training Specifics

The Critical Workout

The brick run is your most important Ironman-specific session.

Progression:

Brick Run Execution

First 10 minutes:

• Walk out of T2
• Very easy jog
• Let legs adapt
• Don't panic at heavy feeling

Minutes 10-20:

• Gradually increase effort
• Find running rhythm
• Check in with body
• Start nutrition intake

Remainder:

• Settle into target pace
• Practice aid station routine
• Mental rehearsal for race
• Build if feeling good

More details: Brick Workouts Triathlon

Race Day Run Strategy

Pacing Approach

The rule: Start slower than you think you should.

Aid Station Strategy

At every station:

1. Walk through (don't run through)
2. Grab water and sports drink
3. Drink while walking
4. Take gel/nutrition if scheduled
5. Dump water on head/neck (if hot)
6. Resume running after station

Time cost: 15-30 seconds per station Energy saved: Enormous

Run/Walk Strategy

Legitimate strategy for many:

Walk breaks work because:

• Reduce cumulative fatigue
• Allow proper nutrition intake
• Can produce faster overall times
• More sustainable mentally

Guide: Triathlon Run Walk Strategy

Ironman Run Nutrition

Fueling Targets

What Works on the Run

Usually tolerated:

• Gels (caffeinated help late)
• Sports drink
• Cola (flat is better)
• Pretzels, chips (salt)
• Banana pieces

Often problematic:

• Solid bars
• Fatty foods
• Large volumes at once
• New products

Hydration

• Drink at every aid station
• Don't overdrink
• Take electrolytes
• Ice/sponges for cooling

Common Run Challenges

Challenge 1: Dead Legs at Start

Normal. Your legs will feel terrible initially.

Solutions:

• Start very slowly
• Walk first aid station
• Trust it will improve
• Usually better by km 5

Challenge 2: GI Distress

The problem: Hours of racing stress the gut

Solutions:

• Don't overdrink
• Walk when drinking
• Try cola instead of gels
• Reduce intake if severe

Challenge 3: Cramping

Causes: Fatigue, dehydration, electrolyte imbalance

In-race solutions:

• Walk briefly
• Take salt/electrolytes
• Stretch gently
• Reduce pace

Challenge 4: Mental Low Points

Everyone experiences them. Usually km 20-35.

Solutions:

• Break into smaller chunks
• Use mantras
• Draw on crowd energy
• Remember your training
• Focus on next aid station

More on mental game: Ironman Mental Preparation

Form Under Fatigue

Key Form Cues

Posture:

• Tall spine
• Slight forward lean from ankles
• Eyes forward, not down
• Relaxed shoulders

Cadence:

• Maintain 170-180 steps/min
• Short, quick steps
• Light footstrike
• Don't overstride

Arms:

• Relaxed, 90-degree bend
• Forward-back motion
• No cross-body swing
• Hands loosely cupped

Form Checkpoints

Every 2-3 km, check:

• Am I running tall?
• Are my shoulders relaxed?
• Is my cadence quick?
• Am I breathing smoothly?

More on form: Triathlon Run Cadence

Sample Training Week

Build Phase Week

Related Resources

• Ironman Time Calculator - Race prediction
• Half Marathon Pace Calculator - Base pace
• Running Off the Bike - Transition running
• Brick Workouts Triathlon - Key sessions
• Ironman Nutrition Guide - Race fueling
• 24-Week Ironman Plan - Complete program