Ironman 70.3 Pacing Strategy: How Much Reserve to Keep in the Swim, Bike, and Run

70.3 Distance Recap

• Swim: 1.9 km
• Bike: 90 km
• Run: 21.1 km (half marathon)
• Expected finish time: 5:00-7:30 (median around 6:00)

Heart Rate and Power Zone Recommendations for the Three Legs

Key principle: Intensity should rise gradually from swim to run. The most common mistake is riding at 80% FTP on the bike leg to chase time, then blowing up completely on the run.

Swim Leg: Hold RPE 6

For a seasoned athlete, 1.9 km takes about 30-38 minutes. Pacing key points:

• First 200m: Deliberately slow, blend into the crowd (avoid heart rate spiking to 90%)
• Middle 1500m: Steady pace at about 1:55-2:05 per 100m
• Final 200m: Exit steadily, no sprint

Tip: Breathe every 6 strokes, sight once per lift of the head, and check the course marker every 200m.

T1 Transition: Don’t Skimp on 30 Seconds

Many people sprint out of the swim zone in 1 minute to chase position, only to forget:

• Putting on the GPS watch
• Taking a sip of water
• Confirming the nutrition bag is loaded on the bike correctly

Reasonable T1 time: 3-5 minutes. A 1-minute difference means little to total time, but a missing nutrition bag means a lot.

90 km Bike Leg: FTP 65-75% Rule

Baseline Pacing

If FTP = 250 W:

• Flat-road target NP (Normalized Power) = 162-188 W
• Short bursts on climbs can go up to 210 W, but must return to average within 5 minutes
• VI (Variability Index) ≤ 1.05 is ideal

Nutrition Rhythm

Eat every 20-25 minutes:

• 0:30: 100 ml isotonic drink
• 1:00: Energy gel with 30g carbs
• 1:30: 100 ml water + salt tablet
• 2:00: Half an energy bar

90 km takes about 2:30-3:00 to complete, with a total intake target of 60-90 g carbs/hour.

Top Pacing Mistakes

1. Too much effort in the first 30 km: Fresh off the swim with adrenaline, athletes unknowingly ride at 80% FTP
2. Failed pack riding: Drafting is strictly prohibited in 70.3 (draft distance 12m); riding too close results in penalties
3. Not pedaling on descents: Downhills are a free opportunity to save glycogen—don’t coast

T2 Transition: Rehydrate and Replenish Salt

T2 is more critical than T1 because the toughest run leg comes next. Recommendations:

• Drink 250 ml isotonic + 1 salt tablet
• Apply Vaseline to inner thighs (anti-chafing)
• Put on a running cap (sun protection)

21.1 km Run: Break It Into Three Segments

0-7 km: Suppress the Urge

Legs feel stiff after getting off the bike, and pace often “feels slow but is actually fast.” Recommendations:

• Target heart rate = Bike leg average + 5-8 bpm
• Pace 10 sec/km slower than target
• Keep RPE at 7

7-14 km: Find Your Rhythm

The body adapts to the running motion; bring target pace back on track:

• Marathon pace + 10-15 seconds
• Drink at every water station (every 5K)
• One energy gel every 7-8 km

14-21.1 km: The Willpower Zone

In the final 7 km, heart rate rising to 85-88% HRmax is normal, but pace should not drop. Willpower techniques:

• Break it into seven 1K segments, count steps in each 1K
• Pour water over your head at every water station to cool down
• Count down the last 3K: burn all remaining energy

Total Nutrition Estimate

A 70.3 burns 4000-5500 kcal in total; recommended intake:

• Carbohydrates: 200-300 g total (120-180g on the bike leg, 60-90g on the run leg)
• Salt: 1000-1500 mg
• Water: 3-4 L

Conclusion

70.3 is not about “giving everything you have,” but about “keeping 5% reserve in each leg for the next one.” Athletes who can still accelerate in the final 7 km of the run will always beat those who rode too hard in the first 60 km.

Related Reading

• 70.3 Half Ironman Finish Guide: Breakthrough Rhythm for Middle-Distance Athletes
• IM 70.3 Finish Pacing Calculator — Precise Power and Heart Rate Configuration for Swim/Bike/Run
• IRONMAN 70.3 Distance Fully Explained: How to Estimate Finish Time for 1.9/90/21.1 km
• IRONMAN Marathon Pacing at 7:00-7:30/km: Segment Strategy and Walk-Break Techniques