Pacing Your Long Distance Duathlon (20/80/10)

Race as One Continuous Effort

A long-distance duathlon (20 km run → 80 km bike → 10 km run) is often 4 to 8 hours of effort. 

You should treat it as one continuous race rather than three detached segments. Planning and pacing matter — go too hard early and it will cost you later.

Run 1 — A Steady Start, Not a Fast 20 K

The first 20 km should feel more like a steady long run (similar to marathon pace), not an all-out 20 K race. 

Target intensity for Run 1 (adjusted depending on expected finish time)

Why this conservative start helps:

• It preserves energy for the bike.

• Keeps your heart-rate and effort manageable, avoiding early over-stress.

• Leaves the possibility to optimise Run 2 if you feel strong later.

As with any duathlon: use a mix of pace, heart-rate, and feel (RPE) to guide effort — none is foolproof, especially over many hours.

Bike Leg — Discipline, Not “Go-Hard”

The bike section is the most critical leg for pacing discipline. If you ride too hard, the final run will suffer. 

Bike pacing targets by expected race duration:

Common mistakes to avoid:

• Trying to hold a constant power that’s slightly too high — what feels manageable early will drain you later. 

• Surging or riding in bursts rather than staying steady. 

• Over-pushing hills due to heavy gearing. 

A controlled bike effort helps:

• Keep your legs fresh for Run 2,

• Aid digestion and nutrition uptake,

• Allow you to run better off the bike when many others will be fading. 

Run 2 (10 K) — Smart Finish, Controlled Effort

After the bike, the final 10 km run will be demanding — the earlier cumulative fatigue will show up here. A controlled but smart finish gives you best shot. 

Run 2 pacing targets: 

When you exit T2: settle in gently, rehydrate or eat if needed — don’t sprint out. Once pace feels sustainable, maintain rhythm and, if you feel good near the end — push to finish strongly. 

Core Principles to Remember

• Use recent, real fitness data, not guesses — any thresholds or pace targets should come from tests done in the last ~8 weeks. 

• Treat the event as one long race, not three separate disciplines — pacing and energy management matter for overall completion as much as split times. 

• Use combined pacing metrics — pace, heart rate and perceived effort. Conditions, terrain and fatigue will affect each; none alone is reliable across 5–8 hours. 

• Nutrition, hydration & discipline on the bike are critical — a smart ride often determines the quality of the final run.