10 Ironman 70.3 Zone 4 / Threshold Example Brick Sessions

Summary:
Ironman 70.3 threshold brick training, typically performed at 91–105% of FTP, 87–93% of maximum heart rate or an RPE of 7–8, plays a key role in Ironman 70.3 preparation by developing the ability to sustain high controlled output while rehearsing the demands that appear when moving from bike to run. These sessions sit above tempo and close to the upper boundary of sustainable intensity, allowing athletes to build resilience under pressure without losing structure. Rather than chasing exhaustion, Zone 4 bricks strengthen pacing discipline, mechanical control and tolerance to sustained discomfort, helping athletes begin the run composed and stable.

Why Ironman 70.3 Threshold Brick Training Matters

Ironman 70.3 brick sessions reflect the demands of triathlon by placing the run immediately after the bike, allowing athletes to practise managing fatigue that carries across disciplines. Threshold training can play a valuable role within Ironman 70.3 preparation and when applied in this format it helps athletes practise sustaining high controlled output while preparing for the demands of the run that follows. It is used to raise the ceiling of sustainable effort so work performed at lower intensities can be held for longer with greater control and less accumulated strain. When included appropriately, threshold work strengthens the systems that support endurance performance, helping efficiency and resilience develop together across a training block.

Zone 4 training targets an intensity that challenges an athlete’s upper sustainable limit. During this phase, lactate accumulation continues to increase to the point where it is around one’s lactate threshold. Repeated exposure to this workload improves durability, increases the output that can be sustained below threshold and enhances tolerance to sustained pressure. Structured threshold brick sessions also reinforce smooth cadence and concentration under load, supporting stable and repeatable execution from bike to run.

This may help you: Triathlon Training: What Is Zone 4 / Threshold Workouts?

Metrics Guide for Ironman 70.3 Threshold Brick Training

Understanding how Ironman 70.3 threshold brick training is measured helps ensure sessions are executed at the correct intensity and deliver their intended effect. The following metrics are used to define and monitor Zone 4 work with clarity and consistency.

Heart rate measures how frequently the heart beats per minute and reflects the body’s internal response to effort. In training, it is used to estimate how hard the cardiovascular system is working relative to an athlete’s maximum or threshold heart rate. FTP or Functional Threshold Power represents the highest average power an athlete can sustain at threshold intensity for approximately one hour and is used as a reference point for defining cycling zones and expressing intensity relative to sustainable effort. RPE or Rate of Perceived Exertion describes how hard a session feels to the athlete on a subjective scale and provides a practical reference for translating internal sensations of effort into usable training intensity.

Threshold Brick Metrics

• Heart Rate (Zone 4): 87–93% of max HR

• Bike Power (FTP): 91–105% of FTP

• RPE: 7–8 out of 10

• Effort: Hard

• Use the FLJUGA Heart Rate Calculator to find your exact training zones.

These metrics define the upper boundary of sustainable intensity and help keep threshold sessions precise rather than reactive. Staying within the outlined ranges ensures work remains challenging without tipping into excessive strain. Over time, this allows threshold training to improve durability, raise sustainable output below threshold and increase tolerance to sustained pressure from bike to run. When intensity is clearly defined and consistently respected, threshold sessions become a reliable tool for long-term progression rather than isolated hard efforts that compromise recovery or training balance.

This may help you: Triathlon Training Zones 1–5 Explained: Why They Matter

10 Example Ironman 70.3 Threshold Brick Sessions

1. Split Threshold Brick

• Purpose: Break threshold into repeatable chunks for quality effort

• Bike Warm-Up: 10 min spin

• Bike Main Set: 2 x 8 min @ Zone 4 (4 min easy spin between)

• Transition Jog: 5 min easy jog

• Run Main Set: 3 x 5 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: 10 min spin

• Bike Main Set: 10 min @ Zone 2 + 10 min @ Zone 3 + 6 min @ Zone 4

• Transition Jog: 5 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: 10 min spin

• Bike Main Set: 6 x 4 min @ Zone 4 (3 min easy spin between)

• Transition Jog: 5 min easy jog

• Run Main Set: 4 x 4 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: 10 min spin

• Bike Main Set: 2 x 8 min @ Zone 4 (5 min easy spin between)

• Transition Jog: 5 min easy jog

• Run Main Set: 2 x 6 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: 10 min spin

• Bike Main Set: 4 / 6 / 4 min @ Zone 4 (3 min easy spin between)

• Transition Jog: 5 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: 10 min spin

• Bike Main Set: 2 x (6 min @ Zone 4 + 10 min @ Zone 3) (3 min easy spin between)

• Transition Jog: 5 min easy jog

• Run Main Set: 2 x (5 min @ Zone 4 + 10 min @ Zone 3) (2 min easy jog between)

• Cool-Down: 10 min jog

7. Short Threshold Brick

• Purpose: High intensity in low volume to reduce fatigue while maintaining load

• Bike Warm-Up: 10 min spin

• Bike Main Set: 4 x 5 min @ Zone 4 (2 min easy spin between)

• Transition Jog: 5 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: Practise precise changes in intensity while remaining controlled

• Bike Warm-Up: 10 min spin

• Bike Main Set: 2 x 6 min alternating 2 min @ Zone 4 and 1 min @ Zone 3 (2 min easy spin between)

• Transition Jog: 5 min easy jog

• Run Main Set: 2 x 6 min alternating 2 min @ Zone 4 and 1 min @ Zone 3 (2 min easy jog between)

• Cool-Down: 10 min jog

9. Brick Simulation Threshold Set

• Purpose: Practise lifting into threshold after sustained load

• Bike Warm-Up: 10 min spin

• Bike Main Set: 40 min @ Zone 2 + 8 min @ Zone 4

• Transition Jog: 5 min easy jog

• Run Main Set: 10 min @ Zone 4

• Cool-Down: 10 min jog

10. Tempo into Threshold Brick

• Purpose: Start controlled, then shift into peak effort

• Bike Warm-Up: 10 min spin

• Bike Main Set: 15 min @ Zone 3 + 6 min @ Zone 4

• Transition Jog: 5 min easy jog

• Run Main Set: 15 min @ Zone 3 + 6 min @ Zone 4

• Cool-Down: 10 min jog

Common Mistakes with Ironman 70.3 Threshold Brick Training

Ironman 70.3 threshold brick training can be one of the most effective tools for improving performance capacity, but only when it is applied with restraint and consistency. Because Zone 4 work feels productive and measurable, it is easy to misuse or rely on it too heavily. These mistakes often reduce the quality of training and limit long-term progression rather than accelerating it.

• Working too hard too often:
  Threshold work is demanding yet controlled, not an all out effort. Pushing beyond the intended intensity too frequently increases fatigue, compromises recovery and often reveals itself once athletes begin the run. Threshold sessions are most effective when they remain repeatable rather than maximal.

• Skipping recovery sessions:
  Hard work places significant stress on the body and requires appropriate recovery to be effective. Neglecting easier training or rest days limits adaptation and increases injury risk. Recovery allows threshold bricks to deliver their intended benefit rather than accumulate fatigue that carries into subsequent sessions.

• Neglecting pacing:
  Threshold intervals require steady and disciplined effort. Spiking power early or surging mid interval reduces time spent in the intended zone and lowers the quality of the work that follows after transition. Controlled pacing keeps execution stable from bike to run.

• Poor fuelling practice:
  Zone 4 sessions can place meaningful demands on energy availability. Inadequate fuelling often becomes obvious when athletes try to stabilise rhythm on the run. Threshold bricks provide an opportunity to practise nutrition under sustained load rather than leaving fuelling untested.

When used correctly, threshold training builds durability and confidence without overwhelming the system. When intensity is respected, pacing remains controlled and recovery is prioritised, threshold work becomes a reliable tool for long-term progression rather than a source of unnecessary fatigue.

This may help you: How to Train for Ironman 70.3: The Complete Training Guide

FAQ: Ironman 70.3 Threshold Brick Training

What is a Zone 4 threshold brick in Ironman 70.3 training?
A threshold brick combines high controlled bike intensity with a run immediately after, helping athletes practise sustaining pressure while maintaining organisation across disciplines.

How hard should Ironman 70.3 threshold bricks feel?
Effort should feel hard but controlled at an RPE of 7–8, allowing athletes to work near their sustainable limit without losing composure.

Is threshold harder than tempo in Ironman 70.3 preparation?
Yes. Zone 4 sits above tempo and close to the upper boundary of sustainable intensity, making it more demanding and requiring greater recovery.

How often should threshold bricks be used in Ironman 70.3 training?
Frequency depends on where an athlete sits within a training plan, their endurance background, their current fitness and their ability to recover between sessions.

Why is pacing important in Ironman 70.3 threshold bricks?
Steady output on the bike strongly influences how stable and controlled the run will feel after transition.

Should I feel exhausted starting the run in an Ironman 70.3 threshold brick?
No. Athletes should feel challenged yet organised, capable of running with structure rather than reacting to fatigue.

What is the main benefit of Zone 4 brick training for Ironman 70.3?
It improves durability, raises sustainable output and builds confidence in handling pressure from bike to run.

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

Ironman 70.3 threshold bricks offer athletes a structured way to practise sustaining high controlled output while preparing for the demands that follow from bike to run. When placed carefully within a programme, Zone 4 work can improve durability, sharpen pacing awareness and build confidence in managing pressure without overwhelming recovery. The value of these sessions comes from precision and repeatability, allowing athletes to experience meaningful intensity while maintaining organisation across disciplines. Applied with patience and respect for load, Ironman threshold bricks become a dependable part of long-term preparation.

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.