In a triathlon you run on legs that were just cycling. That’s a problem of coordination, not fitness, and it’s exactly what bricks train. They also show whether your bike target leaves enough in your legs for the run.
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 a race the order is 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, 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.
At race pace (~80% of your race targets).
Long-course (70.3 and Ironman): race-pace bike and run in late build and peak. Short-course (Olympic and sprint): threshold bike in multi-repeat build bricks; race-pace simulation in peak.
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 weeks).
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 for how phases fit the full plan.
Practise your transitions when you can. T2 is on the clock too.
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 your [zone](/guides/triathlon-training-zones) targets until your stride settles.
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 shows whether your brick work translated — or whether you still rode too hard.
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.