Ironman Training: 10 Zone 4 / Threshold Run Workouts
Summary:
These Zone 4 / threshold workouts target 87 to 93% max heart rate at an RPE of 7 to 8. They strengthen your ability to manage rising effort, clear lactate and stay in control when pace begins to press. Threshold training improves the stability of your form during harder running and helps you maintain purposeful speed late in the Ironman marathon. You finish stronger because the intensity feels more familiar and more manageable.
Zone 4 Marathon Threshold Workouts
Threshold running is the point where controlled effort begins to test your ability to stay composed. Zone 4 sessions place you just below your red line so you can develop the capacity to manage rising discomfort without losing rhythm. This intensity lifts your lactate threshold and creates improvements that carry across all training zones. As each zone becomes more efficient you gain the ability to settle into Ironman race pace with greater control and more consistent form. This guide outlines ten Zone 4 workouts that build strength you can rely on during the marathon.
Why Threshold Training Matters for the Marathon
Marathon success is not built on long runs alone. To progress you must train the systems that allow you to hold pace when fatigue begins to rise. During this phase lactate accumulation continues to increase to the point where it is around one’s lactate threshold. Threshold running targets this narrow point just below where lactate begins to build faster than you can clear it. In practical terms it is the hardest pace you can sustain for 20–60 minutes and it sits firmly within Zone 4. It is not Ironman race pace but it raises the qualities that make Ironman pace feel steadier and more efficient.
Training in this zone builds:
Lactate clearance capacity: It improves your ability to manage rising lactate and stay composed.
Pacing control at high aerobic loads: It strengthens your ability to hold a set effort without drifting.
Mental resilience during extended effort: It teaches you to stay focused when discomfort begins to rise.
Efficiency at or near marathon pace: It helps you maintain form and rhythm when the effort becomes more demanding.
Threshold work strengthens your ability to stay composed when the effort begins to rise. You learn to manage discomfort without losing rhythm, which makes marathon pace feel more manageable. This becomes especially valuable late in the race when form starts to tighten, pace begins to drift, and holding shape becomes more challenging. With stronger threshold conditioning you maintain purposeful movement deep into the final stretch.
What Is Zone 4 Running?
Zone 4 is the intensity where running becomes controlled but demanding. Breathing grows heavier, focus sharpens and each stride requires attention to stay steady. This is often called the lactate threshold zone because it targets the point where lactate begins to rise more rapidly and your body must work harder to clear it. Training here teaches you to sustain strong running without tipping into an unsustainable effort.
Zone 4 typically sits at:
87 to 93% max heart rate: A strong, committed effort that requires concentration.
RPE 7 to 8: Hard running that remains stable when managed well.
Around 5K pace: Fast enough to challenge your control but not an all out effort.
Threshold pace is not Ironman marathon pace. It sits far above it. The role of Zone 4 is to improve how efficiently you clear lactate so that every lower zone becomes easier to maintain. When this system adapts, efforts that once felt demanding begin to settle and extended running in Zones 2 and 3 becomes more sustainable across long training blocks or race day.
Use the FLJUGA calculator to calculate your zones.
10 Threshold Sessions for Marathon Training
1. Classic Threshold Blocks
Purpose: Build lactate control with repeatable Zone 4 efforts
Warm-Up: 15 min jog
Main Set: 3 x 10 min @ Zone 4 (3 min jog between)
Cool-Down: 10 min jog
2. Long Threshold Finish
Purpose: Practice pushing threshold when tired
Warm-Up: 15 min jog
Main Set: 70 min @ Zone 2 – 20 min @ Zone 4
Cool-Down: 10 min jog
3. Split Threshold Sets
Purpose: Make long reps mentally and physically manageable
Warm-Up: 12 min jog
Main Set:
2 x (6 min @ Zone 4 – 2 min jog – 4 min @ Zone 4 – 2 min jog – 2 min @ Zone 4) (2 min jog between sets)
Cool-Down: 10 min jog
4. Progressive Threshold Run
Purpose: Build into Zone 4 for controlled fatigue resistance
Warm-Up: 10 min jog
Main Set: 10 min @ Zone 2 – 10 min @ Zone 3 – 20 min @ Zone 4
Cool-Down: 10 min jog
5. Broken Threshold Repeats
Purpose: Short recoveries challenge repeatability at threshold
Warm-Up: 15 min jog
Main Set: 6 x 6 min @ Zone 4 (1 min jog recoveries)
Cool-Down: 10 min jog
6. Cruise Interval Session
Purpose: Develop rhythm and repeatable pace
Warm-Up: 15 min jog
Main Set: 5 x 8 min @ Zone 4 (2 min jog between)
Cool-Down: 10 min jog
7. Pyramid Threshold Set
Purpose: Pace control across varying durations
Warm-Up: 15 min jog
Main Set: 5 min – 10 min – 15 min – 10 min – 5 min @ Zone 4 (2 min jog between)
Cool-Down: 10 min jog
8. Marathon Pace + Threshold Combo
Purpose: Transition between race pace and controlled threshold
Warm-Up: 15 min jog
Main Set: 20 min @ Zone 3 – 20 min @ Zone 4
Cool-Down: 10 min jog
9. Alternating Threshold Blocks
Purpose: Mix steady efforts with threshold surges
Warm-Up: 15 min jog
Main Set: 5 x (4 min @ Zone 3 – 4 min @ Zone 4)
Cool-Down: 10 min jog
10. Big Block Threshold
Purpose: Simulate sustained race effort
Warm-Up: 15 min jog
Main Set: 40 min continuous @ Zone 4
Cool-Down: 10 min jog
FAQ: Threshold Training in Ironman Plans
What exactly is Zone 4 / Threshold training for marathon runners?
It’s structured running at lactate threshold. Where your body works hard but stays just under the tipping point of fatigue. Zone 4 effort.
When should I do these sessions?
Once a week, ideally 2–3 days away from your long run.
Should I go by pace, heart rate, or feel?
Use all three. Heart rate and pace give structure, but perceived effort is the best guide when conditions vary.
How long should threshold intervals be?
Start with 5–10 minute intervals and build toward longer blocks of 20–40 minutes.
What if I can’t hit the pace?
Focus on effort, not perfection. The point is to work at a sustained “hard but controlled” intensity.
FURTHER READING: BUILD YOUR MARATHON BASE
Running: Running Zones 1–5 Explained
Marathon Training: 10 Zone 3 / Tempo Workouts
Marathon Training: 10 Zone 5 / VO5 Max Workouts
Marathon Training: 10 Essential Sessions
Marathon Training: What Is Zone 4 / Threshold?
Final Thoughts
Threshold sessions are one of the most powerful tools marathoners can use to build speed and durability. These Zone 4 workouts target your body’s ability to clear lactate and hold effort under pressure, exactly what you need in the second half of the race. By adding these sessions into your weekly schedule, you’ll not only run faster, but smarter. Use them consistently, listen to your body and watch your marathon pace start to feel easier over time.
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.
