Triathlon requires your body to run on legs that were just cycling. Brick training rehearses that switch before the start line — and shows whether your Race Pacing Targets on the bike leave enough run for the second half. That is a neuromuscular switch problem, not a fitness gap — and it is what bricks are designed to solve. For T1/T2 kit and transition layout on race day, see Your First Triathlon Explained.
Why bricks
Why Legs Feel Like Bricks
Cycling favours quads and a shorter hip range. Running needs glutes, longer stride, and a different kinetic chain. For 30 seconds to several minutes your nervous system still fires for cycling — you run inefficiently until the pattern updates.
More rehearsed transitions mean faster normalisation. That is the entire point of brick training.
Definition
What a Brick Session Is
Two disciplines back-to-back with minimal rest. In racing, legs go swim → bike → run; in training, bike → run bricks deliver the most run-specific adaptation. Swim → bike sessions help T1 rhythm with less carry-over to the run.
On WattX, brick sessions are built into your WattX Race Plan PRO from build onward — progressive formats through build, then a simulation brick every peak week, scaled to your distance.
Formats
Brick Formats
Endurance ride → endurance run.
Builds fatigue on the bike, then teaches pacing on heavy legs. Used in build and long-course peak — not in base.
Long-course (70.3 and Ironman): sweet spot on bike and run in late build and every peak week. Short-course (Olympic and sprint): threshold bike in multi-repeat build bricks; simulation brick every peak week. Not in base.
Olympic: 4 × (15 min bike / 10 min run). Sprint: 2–3 × (10 min bike / 5 min run).
Many switches per session — neuromuscular learning for short-course in build.
70.3 ~3 h bike → 90 min run · Ironman ~5 h bike → 2 h run.
Long-course simulation in peak; shorter scaled versions in build on brick weeks (70.3 and Ironman alternate brick weeks with long ride).
Scheduling
Scheduling in Your Week
Short-course (sprint and Olympic): build — multi-repeat bricks (15/10 Olympic, 10/5 sprint); peak — simulation brick every week.
Long-course (70.3 and Ironman): build — fatigue-resistance or long bricks on brick weeks, long ride on alternate weeks; peak — simulation brick at race-specific duration every week.
See Race Planning Explained for how phases fit the full plan.
Practice real transition flow when you can — the clock includes T2.
A WattX Race Plan PRO places build and peak bricks in the right weeks for your distance — including long-ride alternation on 70.3 and Ironman. No bricks in base.
Mistakes
Common Mistakes
Cycling legs make pace feel easier. Hold [Triathlon Training Zones Explained](/guides/triathlon-training-zones) targets or power until stride normalises.
20 minutes often suffices off the bike. Save long runs for standalone endurance sessions.
Start at least 8 weeks out for 70.3 — the switch needs repetition.
One per week is plenty for most age-group athletes.
Pacing tie-in
Tie-In to Pacing and Analysis
Bricks rehearse the same percentages as your Race Simulator and Race Pacing Targets.
After race day, Race Analysis Explained shows whether your brick work translated — or whether the bike was still too hot.
Keep CSS, FTP, and FT up-to-date on Threshold Testing — or sync from a clean race in the Race Vault. Protocols: How to Test Your Thresholds.