Open Water 90-Minute Zone 2 Endurance Swim

Session Overview

This 90-minute open water session develops the aerobic endurance base needed for 70.3 and Ironman swim legs. Staying in Zone 2 throughout, you’ll log continuous time in the water to build efficiency, confidence, and fatigue resistance under realistic race conditions.

What You’ll Need

• Open water venue with marked course or GPS swim watch
• Wetsuit (optional if water temperature is above 22°C)
• Open water safety buoy
• Swim partner or kayak support (strongly recommended)

Warm-Up (10 minutes)

Enter the water gradually and begin with 10 minutes of easy freestyle with no pace targets — just feel. Focus on settling your breathing, adjusting to the water temperature, and establishing a comfortable bilateral breathing rhythm before the main effort begins.

Main Set

Swim continuously for 70 minutes at a comfortable aerobic pace — you should feel like you could speak if you paused. Aim for smooth sighting every 8-10 strokes and a consistent stroke rate throughout. Break the effort into three mental phases to stay engaged.

• 0-20 min: settle into Zone 2, establish your sighting rhythm and breathing cadence
• 20-60 min: steady aerobic cruise, long efficient strokes, minimise drift
• 60-70 min: hold pace or nudge slightly harder — don’t fade on the way back to shore

Cool-Down (10 minutes)

Exit at 80 minutes and spend 10 minutes stretching on the bank — prioritise shoulders, chest, and hip flexors. If still in the water, switch to backstroke for the final 5 minutes to open up your chest and decompress after a sustained prone position.

Coaching Notes

• Zone 2 should feel like RPE 5-6/10 — you’re working aerobically but could continue for much longer.
• If your form breaks down before 60 minutes, that’s your current endurance ceiling — build from there week by week.
• Beginners: start with 45-60 minutes continuous open water swimming and add 10-15 minutes per week to reach 90 minutes.
• Never swim open water alone — always use a swim buddy or inform someone of your plan and expected finish time.