Ironman Bike Training: 10 Zone 4 / Threshold Workouts
Summary:
Zone 4 cycling sits at 91–105% of FTP and 87–93% of max heart rate (RPE 7–8). This is the threshold zone where Ironman cyclists build sustainable power and race-day control. Training in Zone 4 improves your ability to hold effort over long periods, clear lactate more efficiently and stay focused under fatigue. These sessions develop muscular endurance, pacing discipline and confidence across the full 180 km bike leg. Include them weekly and turn your bike split into a strength.
What Are Threshold Bike Workouts?
Threshold cycling is a crucial part of Ironman training. It improves sustained power output, pacing efficiency and fatigue resistance across the 180 km (112-mile) bike leg. These sessions help you ride harder for longer without breaking down, making them essential for building a strong, controlled performance on race day.
These sessions focus on Functional Threshold Power (FTP), lactate clearance and race-specific strength to ensure a strong and efficient ride. In this post, you’ll find 10 focused threshold bike sessions for building sustained power, control and race-day strength for Ironman training.
Threshold Bike Metrics (Zone 4)
Use these key performance markers to guide your threshold sessions:
Power: 91–105% of Functional Threshold Power (FTP)
Heart Rate: 87–93% of Max HR
RPE (Effort): 7–8. Hard but sustainable
Use FLJUGA’s free FTP and Heart Rate Calculators to set your exact training zones.
10 focused threshold bike sessions
1. Sustained Threshold
Purpose: Build sustained power in Zone 4
Warm-Up: 15 min spin + 3 x 30 sec fast
Main Set: 2 x 20 min @ Zone 4 (5 min easy spin between)
Cool-Down: 10 min easy spin
2. Threshold Intervals
Purpose: Accumulate Zone 4 time with full control
Warm-Up: 15 min spin
Main Set: 4 x 10 min @ Zone 4 (3 min spin between)
Cool-Down: 10 min spin
3. Ladder Threshold Set
Purpose: Build duration and pacing through ascending and descending reps
Warm-Up: 15 min spin + drills
Main Set: 5 / 10 / 15 / 10 / 5 min @ Zone 4 (2 min spin between)
Cool-Down: 10 min spin
4. Alternating Blocks
Purpose: Stress aerobic control with shifts into Zone 4
Warm-Up: 12 min spin
Main Set: 3 x (5 min @ Zone 2 + 10 min @ Zone 4)
Cool-Down: 10 min spin
5. Split Repeats
Purpose: Break threshold into focused chunks to maintain quality
Warm-Up: 15 min spin + 3 high-cadence efforts
Main Set: 2 x (4 min @ Zone 4 + 3 min easy spin + 4 min @ Zone 4)
Cool-Down: 10 min spin
6. Progressive Build
Purpose: Shift from aerobic work into threshold
Warm-Up: 15 min spin
Main Set: 15 min @ Zone 2 + 10 min @ Zone 3 + 10 min @ Zone 4
Cool-Down: 10 min spin
7. Controlled Surges
Purpose: Practice shifting into Zone 4 without losing control of form
Warm-Up: 15 min spin + 3 x 20 sec high cadence
Main Set: 6 x (2 min @ Zone 3 + 3 min @ Zone 4)
Recovery between sets: 2 min spin
Cool-Down: 10 min spin
8. Long Intervals
Purpose: Improve sustained effort under Ironman fatigue
Warm-Up: 15 min spin + cadence work
Main Set: 3 x 15 min @ Zone 4 (5 min easy spin between)
Cool-Down: 10 min spin
9. Threshold Sandwich
Purpose: Combine endurance and threshold in one set
Warm-Up: 10 min spin
Main Set: 30 min @ Zone 2 + 20 min @ Zone 4 + 10 min @ Zone 2
Cool-Down: 10 min spin
10. Threshold Finish
Purpose: Train threshold fatigue resistance late in the ride
Warm-Up: 10 min spin
Main Set: 90 min @ Zone 2 + 20 min @ Zone 4
Cool-Down: 10 min spin
FAQ: Threshold Bike Training for Ironman
What is threshold power on the bike?
Threshold power is the highest average power you can sustain for about an hour, typically measured as Functional Threshold Power (FTP).
Why is threshold training important for Ironman cyclists?
It improves your ability to clear lactate, builds muscular endurance and helps you hold steady power over long efforts. This makes it essential for staying strong and composed across the 180 km bike leg.
How often should I do threshold bike sessions?
Once per week during your build phase is ideal. Combine with long rides, tempo efforts, and recovery rides for balance.
How long should threshold intervals be?
Intervals typically range from 5 to 20 minutes. Start with shorter reps and increase duration as your fitness builds.
Can I do threshold sessions indoors?
Absolutely. Indoor training allows for precise control over intensity and is great for structured threshold work, especially using a smart trainer or power meter.
FURTHER READING: BUILD YOUR IRONMAN RUN ENGINE
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 Training Threshold Sessions
Ironman Swim Training: 10 Threshold Sessions
Ironman Run Training: 10 Threshold Sessions
Ironman Training: Recovery Week
Ironman Training: Beginner’s Guide
Final Thoughts
These threshold bike sessions play a crucial role in significantly improving your ability to maintain sustained power over long distances, enhancing your race-day pacing strategies and increasing your overall resistance to fatigue during the most demanding parts of the course.
To maximise your Ironman cycling performance, it is highly beneficial to incorporate 1–2 of these carefully focused and structured workouts per week, alongside your regular endurance rides and recovery sessions. This balanced and well-rounded training approach ensures steady progress, builds muscular endurance and helps you achieve optimal conditioning in preparation for race day.
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.
