The short answer
A useful IRONMAN 70.3 brick teaches you to begin running after cycling without turning the session into a test. If you already tolerate both activities, 5–10 easy run minutes after a familiar controlled ride is one starting example. Use less or walk if that exceeds current capacity, and stop for pain or concerning symptoms. Progress duration or specificity one variable at a time.
Research on the cycle-to-run transition reports physiological, biomechanical, and sensory changes after cycling, and a small field study found reduced running distance and shorter stride length after a bike segment compared with an isolated run.1, 2 The exact response differs by athlete. That is why a brick is a rehearsal, not a universal pace prescription.
IRONMAN’s own preparation material recommends practising bike-to-run transitions.3
Four types of brick—and their jobs
| Brick | Example | Job |
|---|---|---|
| Transition brick | Normal ride + 10 min easy run | Learn shoes, posture, and the first kilometre |
| Aerobic brick | Steady ride + 20–40 min easy run | Build repeatable durability |
| Race-specific brick | Race-effort bike segments + controlled run | Test pacing and fueling decisions |
| Logistics brick | Short bike + short run with full transition setup | Rehearse equipment and sequence |
Do not combine all four jobs every week.
An eight-step progression
These are optional coaching examples, not a validated eight-step protocol. Use one step for one or more weeks. Progress only when recovery and the following sessions remain stable.
- 10 minutes easy after an easy ride. Ignore pace; settle breathing and cadence.
- 15 minutes easy after a longer ride. Practise changing shoes and starting calmly.
- 20–25 minutes easy. Keep the first five minutes deliberately restrained.
- Add three short controlled pickups. These are not sprints.
- Practise race fueling on the bike. Change nothing else.
- Add race-effort bike blocks. Keep the run easy.
- Add a short race-effort section to the run. Only after the bike pacing is repeatable.
- Complete one bounded dress rehearsal. Finish knowing what to change, not needing a recovery week.
The first-kilometre rule
The first kilometre should feel almost too controlled. Use it to check:
- Is breathing settling or escalating?
- Can you shorten stride without shuffling?
- Did bike fueling leave your stomach manageable?
- Are shoes, laces, socks, and kit working?
- Is any pain changing your gait?
If the first kilometre is faster than the pace you can sustain, the brick practised the wrong decision.
A brick review card
After the session, write five lines:
- final 30-minute bike effort and conditions;
- fuel and fluid taken;
- transition time and any equipment friction;
- first-kilometre effort, not just pace;
- how the next day’s easy training felt.
This converts a hard-looking session into reusable information.
Progress with gates, not dates
Advance only when all four gates pass:
| Gate | Pass looks like | If it fails |
|---|---|---|
| Movement | Bike handling and run gait remain controlled | Shorten the brick or reduce intensity |
| Fueling | Planned intake is tolerated during and after | Rehearse a simpler intake before adding load |
| Recovery | Normal daily function and easy training return predictably | Repeat or step back |
| Purpose | The session answers one bike-to-run question | Remove extra intervals or stations |
The scientific literature describes real cycle-to-run changes, but most studies are small and do not establish an ideal brick length for every recreational athlete.1, 2 The progression should therefore be driven by what the athlete can repeat.
Worked three-week block
- Week 1: normal aerobic ride plus 10 easy run minutes; learn transition order.
- Week 2: repeat the ride and run; add the planned bike fueling, not more run speed.
- Week 3: keep the ride controlled and add 5–10 run minutes only if the first two bricks settled normally.
Then use an easier week or a non-brick ride to check that specificity is not crowding out recovery. Endurance-recovery and concurrent-training reviews support judging the whole training week, not searching for one recovery trick after overload.5, 6
Use the IRONMAN bike-pacing guide to set the upstream effort and the long-ride recovery guide to make the following-day decision.
Where bricks belong
Most weeks do not need a long or hard brick. A short transition run can follow a ride without adding much complexity. Race-specific bricks deserve more recovery and should not sit beside the hardest long run or heavy lower-body strength work by accident.
Use the IRONMAN 70.3 training hub for the complete cycle and the training start-date calculator to see the runway to your event.
Safety and uncertainty
Use the current competition rules for equipment and transition conduct, including the mount line.4 Fuel and fluid practice should reflect established nutrition guidance and individual tolerance; extra brick minutes are not a reason to force intake.7, 8
Practise on safe routes and follow traffic rules. Heat, terrain, wind, bike fit, fueling tolerance, training history, and health all change the cost of a brick. Stop for chest pain, fainting, severe breathing difficulty, confusion, or acute injury. Persistent pain or gastrointestinal problems deserve qualified assessment.
Frequently asked questions
How long should my first brick run be?
Five to ten easy minutes can answer a transition question for an athlete already comfortable with running and cycling. A shorter exposure may be appropriate; there is no research-established minimum brick duration.
Should the run be at race pace?
Usually not at first. Establish a controlled transition, then add short race-specific work later.
Do I need a brick every week?
Not necessarily. Frequency depends on phase, experience, recovery, and what the session is meant to teach.
Can I do a run-to-bike brick?
It can serve a training purpose, but it does not rehearse the event’s bike-to-run transition.
This guide is educational, not medical advice. Stop and seek appropriate care for chest pain, fainting, severe breathlessness, or pain that changes your movement.
26weeks.ai keeps swim, bike, run, recovery, and disrupted weeks connected to the same finish-line plan. Start training now.
Sources and evidence limits
Sources and associated claims reviewed October 17, 2026. Practical examples are editorial guidance, not individually validated prescriptions.
1 Millet GP et al. Physiological and biomechanical adaptations to the cycle to run transition in Olympic triathlon: review and practical recommendations for training. (2000). Read the source.
2 Olcina G et al. Effects of Cycling on Subsequent Running Performance, Stride Length, and Muscle Oxygen Saturation in Triathletes. (2019). Read the source.
3 IRONMAN. IRONMAN 70.3 pre-race preparation checklist. (Official checklist)
4 IRONMAN. Current competition rules and policies. (Official rules)
5 Li S et al. Effectiveness of Recovery Strategies After Training and Competition in Endurance Athletes: An Umbrella Review. (2024). Read the source.
6 Huiberts RO et al. Concurrent Strength and Endurance Training: A Systematic Review and Meta-Analysis on the Impact of Sex and Training Status. (2024). Read the source.
7 American College of Sports Medicine et al. American College of Sports Medicine position stand. Exercise and fluid replacement. (2007). Read the source.
8 Thomas DT et al. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. (2016). Read the source.