Ironman Pacing Practice: 3-Hour Negative-Split Bike-to-Run Brick

Session Overview

A long brick session built around one specific skill: pacing discipline. Instead of riding steady and then seeing how the legs feel, you deliberately ride the first half conservatively and the second half harder, then carry that same negative-split approach into the run — exactly the pacing shape that separates a strong Ironman-distance finish from a blown-up one.

What You’ll Need

• Power meter or reliable perceived-effort pacing on the bike
• GPS watch for run pace
• Race-day nutrition and hydration (practice exactly what you plan to use on race day)
• Turbo trainer or a safe outdoor loop with minimal junctions (optional)

Warm-Up (15 minutes)

15 minutes easy spinning, building cadence gradually through the last 5 minutes to wake the legs up without spending energy.

Main Set

2 hours 20 minutes on the bike, split into two even blocks either side of your target race power/effort, followed directly by a 40-minute negative-split run off the bike.

• Bike Block 1 (70 minutes): hold 5-10% below your target Ironman/70.3 race power or “comfortably hard, could hold a conversation” effort
• Bike Block 2 (70 minutes): lift to your actual target race power/effort, finishing the last 10 minutes at goal race pace exactly
• Run off the bike (40 minutes): first 20 minutes at 15-20 seconds/km slower than target race pace, second 20 minutes at target race pace

Cool-Down (10 minutes)

10 minutes of easy walking or very light jogging, followed by static stretching for the hip flexors and calves.

Coaching Notes

• The whole point of this session is restraint in Bike Block 1 — if you feel strong and want to push early, that’s exactly the urge to resist.
• Common mistake: treating the run’s first 20 minutes as a throwaway jog rather than a controlled, deliberately-paced effort — it should still feel purposeful, just slower than goal pace.
• Scaling down: for a 70.3-focused athlete, shorten the bike to 90 minutes total (45/45 split) and the run to 25 minutes (12/13 split) at the same relative intensities.
• RPE guidance: Bike Block 1 should sit around RPE 5-6/10, Bike Block 2 around RPE 7/10, and the run’s second half should feel like genuine race effort, RPE 7-8/10.