Open Water Swim: 3.8km Ironman Distance Practice

Session Overview

This session simulates the full IRONMAN swim distance in open water. Covering 3.8km continuously at race-controlled effort, it builds the aerobic endurance, pacing discipline, and mental resilience required for long-course racing. Reserve this session for your peak training phase — ideally 6–8 weeks before your A-race — when your swim fitness is well developed.

What You'll Need

• Wetsuit (if conditions require or your race is wetsuit legal)
• Open water tow float for safety
• GPS watch or open water swim watch
• Support kayak or paddleboard if available
• Sports drink or gel for mid-swim nutrition (practice race-day intake)

Warm-Up (15 minutes)

Enter the water gradually and spend 5 minutes acclimatising to temperature and conditions. Swim 400m easy at very low effort — no pull, just smooth freestyle with focus on breathing rhythm. Include 4 x 25m build efforts to raise heart rate without fatiguing yourself before the main set. Practice your sighting: every 8–10 strokes, lift your eyes just clear of the water to spot a landmark ahead.

Main Set

Swim 3,800m continuously at your target IRONMAN race pace — approximately RPE 6/10, a pace you could sustain for 60–75 minutes. Break the distance mentally into sections to maintain focus:

• First 1,000m: Settle into rhythm, control breathing, find your stroke
• 1,000m–2,500m: Maintain pace, sight regularly, stay relaxed in the shoulders
• 2,500m–3,800m: Focus on technique as fatigue builds. Avoid letting the stroke shorten or the kick reduce to nothing
• Optional: Take one gel or sip of sports drink at the 2,000m mark if practicing race nutrition

Cool-Down (10 minutes)

Swim 200–300m very easy backstroke or catch-up drill, focusing on recovery breathing. Exit carefully — after 3.8km continuous effort, you may feel slightly disoriented standing up. Take 2–3 minutes before moving on to any transition or land-based activity.

Coaching Notes

• Sight every 8–10 strokes — over 3.8km, poor sighting adds hundreds of metres. Practice a quick, clean head lift that doesn't disrupt your stroke.
• Avoid going out too fast in the first 500m. Open water excitement and adrenaline push athletes to swim 10–15% harder than planned. The damage accumulates over the full distance.
• Easier variation: Split into 2 x 1,900m with a 5-minute rest between halves if this is your first long open water session.
• Target RPE 6/10 — you should be able to think and focus on technique, not gasping.