16-Week IRONMAN 70.3 Weymouth Training Plan (Intermediate)

Plan Overview

This 16-week intermediate plan is designed for triathletes targeting IRONMAN 70.3 Weymouth on 20 September 2026. Starting in early June, the plan assumes you can already swim 1km continuously, run 10km comfortably and complete a 2-hour bike ride. By race day, you will have completed multiple long swims, rides up to 90km and long runs up to 18km — fully prepared for the 1.9km swim, 90km bike and 21.1km run that Weymouth demands.

Prerequisites

• Can swim 1km continuously in open water or pool
• Can run 10km comfortably at conversational pace
• Can complete a 2-hour outdoor or turbo bike session
• Comfortable with 8-10 hours of training per week
• Access to a pool, bike (road or tri), running shoes, wetsuit

Plan Structure

The plan follows a structured periodisation model with four distinct phases, progressing from aerobic base building through to race-specific peak fitness before a 2-week taper into Weymouth. Training volume peaks at approximately 12-14 hours per week in weeks 12-13.

• Weeks 1-4: Base Phase — Building aerobic foundation across all three disciplines. Emphasis on technique, consistency and easy aerobic work at 60-70% max HR. Target 8-9 hours per week.
• Weeks 5-9: Build Phase — Introducing tempo and threshold work. Bike rides extend to 70km, run long to 14km. Adding brick sessions. Target 10-12 hours per week.
• Weeks 10-13: Peak Phase — Maximum volume with race-pace work. Long rides to 90km, long runs to 18km, open water swims to 2.5km. Full race simulation in week 12. Target 12-14 hours per week.
• Weeks 14-16: Taper — Volume reduces by 30% in week 14 and 50% in week 15. Week 16 is race week with only short activation sessions. Maintain intensity; cut volume.

Sample Week (Build Phase – Week 7)

This is a typical week from the mid-build phase to give you a sense of the training load:

• Monday: Rest or 20-minute easy swim recovery
• Tuesday: Swim — 2,500m including CSS intervals (e.g., 6 x 200m at CSS pace)
• Wednesday: Run — 50-minute tempo run at 5km pace plus 30 seconds per km
• Thursday: Bike — 90-minute turbo session including 3 x 12 minutes at 80-85% FTP
• Friday: Rest or yoga and mobility work
• Saturday: Long bike — 70km outdoor ride at steady Zone 2-3 effort (around 2.5-3 hours)
• Sunday: Brick — 45-minute easy bike followed immediately by 30-minute run at goal race pace

Key Tips for Success

• Consistency beats intensity — missing 1-2 sessions per week across the plan will not derail you; skipping whole weeks will. Prioritise showing up, even for a reduced session.
• Listen to your body — if you feel genuine fatigue (not normal tiredness), take an extra recovery day. 70.3 training builds significant cumulative load; honour your body signals.
• Practice your race nutrition — train your gut to absorb 60-90g of carbohydrate per hour on long sessions. Do not use race day to try anything new.
• Weymouth-specific prep — the Weymouth bike course is rolling with some notable climbs. Include hilly rides and climbing-specific turbo sessions in your build phase to prepare your legs.