Ironman Brick Training: 10 Threshold Sessions

Summary
Zone 4 training targets your lactate threshold, where lactate is produced quickly but can still be cleared. For Ironman athletes, this means working at 87–93% of max heart rate or 91–105% of FTP. It feels hard but controlled, requiring focus across sustained intervals. Zone 4 sessions raise your threshold, build power and improve pacing control for race day.

Ironman Training: What Are Threshold Bricks? 

Brick workouts, back-to-back sessions that combine cycling and running, are a cornerstone of Ironman preparation. But when performed at Zone 4 threshold intensity, they become a powerful tool for building race-day performance. Threshold bricks challenge your ability to ride and run just below your red line, simulating the sustained pressure you’ll face on race day.

These workouts improve fatigue resistance, lactate clearance and your ability to stay mentally composed under load. They're particularly effective in the build phase, when sharpening your ability to hold strong effort off the bike is essential. Use these sessions to refine your pacing, push your threshold higher, and condition your body and mind to perform when it counts.

Threshold Brick Training Metrics:

• Power (FTP): 91–105% of Functional Threshold Power

• Heart Rate: 87–93% of Max HR

• RPE: 7–8 out of 10 (hard but sustainable)

• Set your FTP and HR training zones with FLJUGA's free tools: FLJUGA Calculator

Why Threshold Brick Workouts Matter

Threshold bricks push you to train near your functional threshold power (FTP) on the bike and your lactate threshold pace on the run. These are the intensities where your body is working hard but sustainably.

Benefits of threshold brick training:

• Enhances your ability to hold strong effort off the bike

• Teaches you to process lactate efficiently

• Builds resilience for the final stretch of the race

• Reinforces race nutrition and pacing strategies

Whether you’re a first-timer or aiming for a new personal best, adding these bricks once per month can elevate your Ironman training.

10 Threshold Brick Sessions

1. Threshold + Tempo Brick

Purpose: Combine threshold bike intervals with steady run pressure

Bike Warm-Up: 15 min spin + 3 cadence lifts
Bike Main Set: 3 x 10 min @ Zone 4 (3 min spin recoveries)
Transition Jog: 10 min easy jog
Run Main Set: 20 min @ Zone 3
Cool-Down: 10 min jog

2. Double Threshold Brick

Purpose: Threshold training in both disciplines under fatigue

Bike Warm-Up: 15 min spin
Bike Main Set: 2 x 15 min @ Zone 4 (5 min easy spin)
Transition Jog: 10 min easy jog
Run Main Set: 3 x 6 min @ Zone 4 (2 min jog recoveries)
Cool-Down: 10 min jog

3. Progressive Threshold Brick

Purpose: Increase intensity through both bike and run

Bike Warm-Up: 12 min spin
Bike Main Set: 10 min @ Zone 2 + 10 min @ Zone 3 + 10 min @ Zone 4
Transition Jog: 10 min easy jog
Run Main Set: 5 min @ Zone 3 + 10 min @ Zone 4
Cool-Down: 10 min jog

4. Split Bike, Strong Run

Purpose: Accumulate controlled threshold work with a strong run focus

Bike Warm-Up: 15 min spin
Bike Main Set: 3 x (5 min @ Zone 4 + 2 min easy spin)
Transition Jog: 10 min easy jog
Run Main Set: 2 x 10 min @ Zone 4 (3 min jog between)
Cool-Down: 10 min jog

5. Extended Threshold Bike + Short Repeats

Purpose: Push threshold duration on the bike, reinforce with short run intervals

Bike Warm-Up: 15 min spin + drills
Bike Main Set: 1 x 30 min @ Zone 4
Transition Jog: 10 min easy jog
Run Main Set: 4 x 3 min @ Zone 4 (1:30 jog recoveries)
Cool-Down: 10 min jog

6. Over-Under Brick

Purpose: Teach pacing shifts into and out of threshold

Bike Warm-Up: 15 min spin
Bike Main Set: 4 x (4 min @ Zone 3 + 6 min @ Zone 4)
Transition Jog: 10 min easy jog
Run Main Set: 3 x (3 min @ Zone 3 + 5 min @ Zone 4)
Cool-Down: 10 min jog

7. Short Threshold Blocks

Purpose: Train short, repeatable threshold efforts across both sports

Bike Warm-Up: 12 min spin
Bike Main Set: 6 x 5 min @ Zone 4 (2 min spin recoveries)
Transition Jog: 10 min easy jog
Run Main Set: 5 x 4 min @ Zone 4 (1 min jog between)
Cool-Down: 10 min jog

8. Ladder Brick Set

Purpose: Layer threshold stress across ascending run and bike sets

Bike Warm-Up: 15 min spin + cadence
Bike Main Set: 8 / 10 / 12 min @ Zone 4 (3 min spin between)
Transition Jog: 10 min easy jog
Run Main Set: 5 / 7 / 9 min @ Zone 4 (2 min jog between)
Cool-Down: 10 min jog

9. Tempo into Threshold Brick

Purpose: Transition from controlled pacing into sustained Zone 4 under fatigue

Bike Warm-Up: 15 min spin
Bike Main Set: 30 min @ Zone 3 + 15 min @ Zone 4
Transition Jog: 10 min easy jog
Run Main Set: 10 min @ Zone 3 + 15 min @ Zone 4
Cool-Down: 10 min jog

10. Long Threshold Finish Brick

Purpose: Practice Zone 4 under deep fatigue

Bike Warm-Up: 15 min spin
Bike Main Set: 90 min @ Zone 2 + 20 min @ Zone 4
Transition Jog: 10 min easy jog
Run Main Set: 20 min @ Zone 4
Cool-Down: 10 min jog

Final Tips for Threshold Brick Training

• Fuel like it’s race day: These sessions burn through glycogen. Use them to practice your race nutrition plan.

• Balance intensity: Follow bricks with easier days or recovery workouts to ensure full adaptation.

• Be consistent: Aim for one threshold brick per week during your race-specific training phase.

• Taper smart: Reduce volume but maintain some intensity in the final 2–3 weeks before your race.

FAQ: Zone 4 Brick Workouts for Ironman Training

How often should I do threshold bricks?

Once a month is ideal during your Ironman build. Combine with VO2 and endurance work for balanced fitness.

Can beginners use these sessions?

Yes. But scale the duration or intensity. Focus on form, consistency and recovery over maximal effort.

Are these good for full Ironman or just 70.3?

They’re ideal for both. Adjust the run and bike durations to suit your goal race distance and fitness level.

FURTHER READING: BUILD BRICK STRENGTH

• Ironman Training: What Is Zone 2 / Endurance?

• Ironman Training: What Is Zone 3 / Tempo?

• Ironman Training: What Is Zone 4 / Threshold?

• Ironman Training: What Is Zone 5 / VO2 Max?

• Ironman Run Training: 10 Threshold Sessions

• Ironman Bike Training: 10 Threshold Workouts

• Ironman Swim Training: 10 Threshold Sessions

• Ironman Training: Recovery Week

• Ironman: Beginner’s Guide

Final Thoughts

Done right, threshold training makes your race pace feel easier, your legs feel stronger and your mindset unbreakable. Use it wisely, and you’ll toe the Ironman start line faster, fitter and more prepared than ever. Zone 4 isn’t just about pushing your limits, it’s about making your limits feel manageable. A few well-timed sessions can elevate your strength, control and race-day confidence. It’s not about intensity for intensity’s sake, it’s about precision, timing and purpose.

Which of these threshold brick sessions will you conquer first?

Always consult with a medical professional or certified coach before beginning any new training program. The information provided is for educational purposes only and is not a substitute for personalized advice.