Ironman 70.3 Training: 10 Zone 4 / Threshold Brick Workouts
Summary:
Threshold brick sessions help Ironman 70.3 athletes build the strength, control and endurance needed to perform under pressure. These workouts target sustained effort at threshold, typically 87–93% of max heart rate, 91–105% of FTP or a 7–8 RPE. By combining controlled intensity across both bike and run, you’ll improve fatigue resistance, pacing precision and mental toughness. Use these 10 sessions to sharpen race execution and develop the resilience to push strong all the way to the finish line.
What Is a Threshold Brick Session for Ironman 70.3?
Threshold brick sessions are some of the most effective workouts for Ironman 70.3 athletes looking to improve speed, endurance and resilience. These sessions focus on sustained efforts at threshold, helping you build the ability to sustain high-intensity work across the bike and run.
By targeting the edge of your sustainable effort, threshold bricks develop physical toughness and pacing precision under fatigue. They train your body to manage lactate, hold strong form and stay mentally engaged when intensity rises, essential skills for closing out a strong 70.3 performance.
Threshold Intensity Guidelines
Threshold sessions focus on high-effort, controlled pacing. Right at the edge of sustainable performance.
Here’s how to track intensity:
Heart Rate (HR): 87–93% of max HR
FTP (Cycling): 91–105% of FTP
RPE (Perceived Effort): 7–8
Use the FLJUGA Zone Calculator to stay dialled into your optimal effort for each session.
Why Threshold Bricks Matter for Ironman 70.3
• Improves Aerobic Capacity – Helps sustain higher power and pace for longer.
• Enhances Bike-to-Run Adaptation – Reduces the heavy-leg feeling off the bike.
• Builds Mental Toughness – Prepares you for race-day discomfort and pacing control.
• Optimises Pacing Strategy – Trains your body to efficiently manage effort levels.
10 Ironman 70.3 Threshold Bricks
1. Split Threshold Brick
Purpose: Break threshold into repeatable chunks for quality effort
Bike Warm-Up: 15 min spin
Bike Main Set: 3 x 10 min @ Zone 4 (4 min easy spin between)
Transition Jog: 10 min easy jog
Run Main Set: 3 x 6 min @ Zone 4 (2 min jog between)
Cool-Down: 10 min jog
2. Threshold Build Brick
Purpose: Progress from steady aerobic to hard controlled effort
Bike Warm-Up: 15 min spin
Bike Main Set: 20 min @ Zone 2 + 15 min @ Zone 3 + 10 min @ Zone 4
Transition Jog: 10 min easy jog
Run Main Set: 10 min @ Zone 2 + 10 min @ Zone 4
Cool-Down: 10 min jog
3. Broken Threshold Repeats
Purpose: Accumulate high-quality Zone 4 time under control
Bike Warm-Up: 15 min spin
Bike Main Set: 6 x 6 min @ Zone 4 (3 min easy spin between)
Transition Jog: 10 min easy jog
Run Main Set: 4 x 5 min @ Zone 4 (90 sec jog between)
Cool-Down: 10 min jog
4. Double Threshold Brick
Purpose: Place threshold effort across both disciplines for deep adaptation
Bike Warm-Up: 15 min spin
Bike Main Set: 2 x 15 min @ Zone 4 (5 min easy spin between)
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. Threshold Pyramid Brick
Purpose: Create varied load through rising and falling reps
Bike Warm-Up: 15 min spin
Bike Main Set: 8 / 12 / 8 min @ Zone 4 (3 min easy spin between)
Transition Jog: 10 min easy jog
Run Main Set: 4 / 6 / 4 min @ Zone 4 (2 min jog between)
Cool-Down: 10 min jog
6. Threshold + Tempo Combo
Purpose: Start strong, hold pressure with Zone 3 finish
Bike Warm-Up: 15 min spin
Bike Main Set: 2 x 10 min @ Zone 4 + 20 min @ Zone 3 (3 min easy spin between)
Transition Jog: 10 min easy jog
Run Main Set: 10 min @ Zone 4 + 15 min @ Zone 3
Cool-Down: 10 min jog
7. Short Threshold Brick
Purpose: High intensity in low volume to reduce fatigue while maintaining load
Bike Warm-Up: 12 min spin
Bike Main Set: 4 x 5 min @ Zone 4 (2 min easy spin between)
Transition Jog: 10 min easy jog
Run Main Set: 4 x 3 min @ Zone 4 (90 sec jog between)
Cool-Down: 10 min jog
8. Over-Under Threshold Brick
Purpose: Prepare for surges and variability in race effort
Bike Warm-Up: 15 min spin
Bike Main Set: 5 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
9. Brick Simulation Threshold Set
Purpose: Simulate final effort intensity of a 70.3 race
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
10. Tempo into Threshold Brick
Purpose: Start controlled, then shift into peak effort
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: 15 min @ Zone 3 + 10 min @ Zone 4
Cool-Down: 10 min jog
Tips for Executing Threshold Bricks
Fuel Strategically – Threshold sessions are demanding; practice race nutrition.
Control Pacing – Stay at prescribed efforts to avoid burnout.
Recover Well – Schedule proper rest after these high-intensity workouts.
Simulate Race Conditions – Use race-day gear and transitions.
Incorporate these threshold brick sessions into your training to develop race-ready fitness and confidence for your next Ironman 70.3!
FAQ: Threshold Brick Sessions
What is a threshold brick session?
It’s a combined bike-run workout where both segments are done at threshold, hard but controlled, to simulate race intensity and build stamina.
Why are threshold bricks important for Ironman 70.3?
They improve your ability to sustain high-effort pacing across long distances, boost muscular endurance and prepare your body for strong bike-to-run transitions.
How often should I do brick workouts?
Once per week during key build phases is ideal. Balance them with recovery and aerobic-focused sessions to avoid overtraining.
What’s the difference between tempo and threshold bricks?
Tempo bricks are moderately hard and sustainable, while threshold bricks push you to race intensity, increasing lactate tolerance and mental toughness.
Can I do these if I’m training for my first 70.3?
Yes. But scale the intensity and distance to your fitness level and build up gradually to avoid injury or burnout.
FURTHER READING: BUILD YOUR 70.3 POWER
Ironman 70.3: What Is Zone 2 / Endurance?
Ironman 70.3: What Is Zone 3 / Tempo?
Ironman 70.3: What Is Zone 4 / Threshold?
Ironman 70.3: What Is Zone 5 / VO2 Max?
Ironman 70.3 Threshold Sessions
Ironman 70.3: 10 Threshold Swim Sessions
Ironman 70.3: 10 Threshold Bike Sessions
Ironman 70.3: 10 Threshold Run Sessions
Final Thoughts
Threshold brick sessions are one of the most powerful tools in your Ironman 70.3 training arsenal. By combining high-intensity efforts on the bike and run, they prepare your body and mind for the demands of race day. Whether you’re aiming for a PR or simply looking to feel strong across all three disciplines, integrating these workouts consistently, while balancing recovery, is the key to unlocking your peak performance. Stick with the process, trust your training and watch your endurance, speed and confidence soar.
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.
