Build Speed Fast: Threshold Swims for Triathletes!
Wondering how to swim faster and more efficiently in your next Ironman race?
Training at threshold pace is key to building the stamina, speed, and confidence needed to tackle the 1.9 km (70.3) or 3.8 km (full Ironman) swim.
Why Threshold Swim Training Matters for Ironman Athletes
Threshold swimming develops the ability to hold a strong pace without excessive fatigue — exactly what you need on race day.
By targeting your Critical Swim Speed (CSS) and working just below your lactate threshold, you improve aerobic endurance, pacing discipline, and stroke efficiency over long distances.
Threshold swim sessions teach your body and mind to maintain form and effort even deep into fatigue — critical for a successful Ironman swim.
These 10 essential threshold swim sessions will sharpen your endurance, improve pacing control, and make you stronger when it matters most!
10 Key Threshold Swim Workouts for Ironman Training
1. Classic CSS Threshold Set
Purpose: Build sustained pacing ability at race effort.
Warm-up:
400m Easy
Main Set:
12 x 100m at CSS pace (15 sec rest)
Cool-down:
200m
Focus: Maintain technique and pace under fatigue.
2. Broken Threshold Intervals
Purpose: Improve threshold endurance with short recovery.
Warm-up:
400m Easy
Main Set:
4 x (200m at CSS + 100m faster than CSS) (20 sec rest)
Cool-down:
200m
Focus: Push through fatigue while sustaining strong effort.
3. Progressive Threshold Swim
Purpose: Train negative splitting and pace control.
Warm-up:
400m Easy
Main Set:
300m at CSS -2s/100m
300m at CSS
300m at CSS +2s/100m
Cool-down:
200m
Focus: Adjust effort smoothly across race scenarios.
4. Threshold & Endurance Combo
Purpose: Blend threshold and aerobic work for race fitness.
Warm-up:
400m Easy
Main Set:
3 x (300m at CSS + 200m at Ironman pace) (30 sec rest)
Cool-down:
200m
Focus: Sustain form and pacing over long distances.
5. Threshold Pacing Challenge
Purpose: Build pacing discipline under growing fatigue.
Warm-up:
400m Easy
Main Set:
4 x 100m at CSS (10 sec rest)
1 x 400m at CSS
4 x 100m at CSS (10 sec rest)
Cool-down:
200m
Focus: Lock in your race pace mentally and physically.
6. Threshold Sprint Finishes
Purpose: Improve finishing strength and mental toughness.
Warm-up:
400m Easy
Main Set:
6 x (150m at CSS + 50m hard effort) (20 sec rest)
Cool-down:
200m
Focus: Teach your body to finish strong even when fatigued.
7. Open Water Threshold Set (Pool or Open Water)
Purpose: Prepare for continuous race efforts.
Warm-up:
400m Easy
Main Set:
3 x 600m at CSS with sighting every 6 strokes (30 sec rest)
Cool-down:
200m
Focus: Maintain pace and form in open-water conditions.
8. Descending Threshold Intervals
Purpose: Train the ability to speed up under fatigue.
Warm-up:
400m Easy
Main Set:
200m at CSS +2s/100m
200m at CSS
200m at CSS -2s/100m
Cool-down:
200m
Focus: Sharpen pace awareness and finishing speed.
9. Strength-Based Threshold Swim (Paddles & Band)
Purpose: Build upper-body strength and race efficiency.
Warm-up:
400m Easy
Main Set:
4 x 150m with paddles + pull buoy at CSS pace (20 sec rest)
4 x 50m with ankle band only (30 sec rest)
Cool-down:
200m
Focus: Strengthen pull and body alignment for long swims.
10. Taper Threshold Tune-Up (7–10 Days Pre-Race)
Purpose: Maintain sharpness without building fatigue.
Warm-up:
400m Easy
Main Set:
3 x 200m at CSS pace (20 sec rest)
6 x 50m at race pace (15 sec rest)
Cool-down:
200m
Focus: Stay smooth, fast, and race-ready.
Final Tips for Threshold Swim Training
Practice Sighting: Even in pool sessions, mix in sighting drills to prepare for open water.
Stay Relaxed Under Pressure: Focus on maintaining good technique even when pushing pace.
Use Consistent CSS Testing: Retest every 4–6 weeks to keep training targeted and effective.
Threshold swim training is essential for developing the strength, pacing, and mental resilience you need to swim your best Ironman race!
FAQs About Threshold Swim Training for Ironman
How often should I include threshold swim sessions?
Most Ironman athletes include 1–2 threshold-focused swim sessions per week, combined with long endurance swims and technique work.
What is Critical Swim Speed (CSS)?
CSS is an estimate of your lactate threshold swim pace — the speed you can maintain without fatiguing too quickly.
Can I do threshold swims in open water?
Yes! Open water threshold sets are great for building continuous endurance under race-like conditions.
Final Thoughts
Threshold swim sessions are the cornerstone of building the endurance, speed, and efficiency you need for Ironman success.
Which threshold swim workout will you tackle first to sharpen your race-day swim performance?
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.