You’ve been told to do a brick every week, and nobody can show you the study that says so. What the research does support is simple: running off the bike feels worse, and a short, steady brick is a cheap way to practice it. How often and how long is mostly coach convention.
That honesty matters. Many articles call bricks “essential” and stop there. This one separates what’s measured from what’s habit, then gives you a plan you can adjust.
A brick workout is a bike ride followed straight away by a run. The name comes from how your legs feel when you start running.
What Happens When You Run Off the Bike
A review by Millet and Vleck pulled together the lab work on this. Running after cycling cost 1.6% to 11.6% more energy than running fresh in Olympic-distance triathletes. Breathing and heart rate also ran higher. In short: the same pace costs you more at the start.
The size of the penalty varied by athlete. Better athletes tended to pay less.
A 2022 study put numbers on the “jelly legs” feeling. Researchers had 22 triathletes run after a 40 km ride. Their runs were unsettled in 82% of trials, versus 32% for a plain run. Stride rate and ground contact time looked normal. The problem was settling, not running style.
Think of a car coming off the highway into a parking lot. The engine is still in highway mode. Your legs are still pedaling, and your lungs are still set for the bike. It takes a few minutes to downshift.
Translation: the first kilometre is the odd one. After that, you mostly run like yourself.
The wider picture is mixed. A 2019 study of 14 middle-level triathletes saw a shorter stride, higher cadence and about 12% higher cost of transport after 30 minutes of cycling. But a study of seven elite triathletes found no running economy penalty after a 20-minute or 50-minute ride. Small groups, different athletes, different answers.
Fitter athletes may simply lose less. That’s a guess, not a finding.
Do Brick Workouts Actually Work?
Here’s the part most articles skip. We found one controlled test of brick training itself. It had 12 collegiate triathletes, split into a brick group and a control group. It was a conference paper, not a journal study. The brick group showed more adaptable knee behaviour and a “positive effect” on the transition, with the mechanism unknown.
Twelve athletes. That’s not a verdict.
So why do coaches use bricks? Practice is cheap, and the first-run feel is real. You also rehearse fueling, shoe changes and pacing under fatigue. Those benefits make sense, even though no trial has measured them.
We also found no controlled study at the full 70.3 distance (90 km bike, 21.1 km run). Most use 20-40 km rides. So every frequency and length number below is convention, and it’s labeled that way.
How Often: Brick Frequency by Phase
Plans and coaches agree on a loose pattern. Roadman Cycling’s Anthony Walsh argues that novices need only one short, easy brick every 7-14 days. A 16-week plan from Lindley and Keat puts a key race-simulation brick every fourth weekend. Others add a second weekly brick in the late build.
Here’s a starting template. It’s convention, not a prescription from a trial.
| Phase | Bricks | Purpose |
|---|---|---|
| Base | 1 every 7-14 days | First-run feel, easy |
| Build | 1 per week, 2 in later weeks | Steady effort, short run |
| Peak | Race-pace brick every ~4th weekend | Pacing and fueling rehearsal |
| Taper | One short brick, 10-15 min run | Stay sharp, nothing new |
Change one thing at a time. Lengthen the ride or the run in a given week. Don’t do both.
How Long: Brick Length by Weekly Hours
USA Triathlon’s samples grow with athlete level. Beginners do 30 minutes of cycling and a 10-minute run. Experienced sprint and Olympic athletes do about 60 and 25. High-performing 70.3 and Ironman athletes do roughly 110 minutes on the bike and 40 running.
Most age-groupers aren’t in that last group. One 12-week plan builds from 60 + 10 minutes to 3 hours + 30 minutes before a 90 + 15 pre-race sim. Forum posters argue over a 2-hour ride with a 1-hour run. Some call it excessive. Others go 2.5 hours + 1.5.
Disagreement like that tells you the number isn’t science.
| Weekly hours | Typical brick | Peak brick |
|---|---|---|
| 4-6 | 45-60 min bike + 10 min run | 90 min + 15 min |
| 6-9 | 60-90 min bike + 10-20 min run | 2 h + 20-30 min |
| 9-12 | 90-120 min bike + 20-30 min run | 2.5-3 h + 30-40 min |
These are stylized suggestions based on the plans above, not tested values. For a race-pace benchmark, one practitioner suggests 56 km on the bike plus 13 km running at race pace before the taper.
Treat the run as real impact load. A long brick run on tired legs costs recovery time. Check the next two days. If they feel clearly worse, the brick did too much.
Small bricks beat heroic ones.
How Hard Should the Bike Be?
Steady power seems to help. One study, whose authors and year we couldn’t confirm, compared constant and variable riding at the same average power. The 5 km run took 1118 seconds after a constant ride. After a variable ride it took 1168 seconds, about 4.5% slower.
Translation: surging on the bike takes something from the run. Ride evenly. A solid zone 2 base helps here. So does knowing your FTP (Functional Threshold Power), the highest power you can hold for about an hour. Here’s how to test it.
Another short-course study, seen only through a summary, reportedly had 38 athletes ride 20 km at 80, 85 or 90% of threshold power, then run 5 km all out. Men ran faster after the easier ride, but their combined time was quicker after the harder one. A 70.3 is far longer, so don’t read that as a reason to ride hard. Race effort is a fixed target.
A Case Study: Dan’s Bricks
Take Dan, 41, a fictional but typical 70.3 athlete with 7 hours a week. In June he did one 90 + 15 brick every week. His first run kilometre came in 25 seconds slower than his fifth. By week 6, he was sore all week and missing his quality run.
He dropped to one brick every 10 days, mostly 60 + 10. He kept one longer race-pace brick every fourth weekend. The first-kilometre gap shrank to 10 seconds. He also stopped skipping his Tuesday run.
Dan’s numbers are illustrative. The pattern isn’t: fewer, better-placed bricks, and an honest check of how the week felt.
When to Skip or Shrink a Brick
Skip the brick if you missed the long ride, slept badly or feel a cold coming. Shrink it to a short, easy version if you’re tired but healthy. Never stack one on top of another hard day.
Check your trend before a big brick. If you’re carrying heavy fatigue, your fitness, fatigue and form scores will show it. Drift in long steady efforts, covered in the aerobic decoupling guide, can warn you that the engine isn’t ready for a long brick yet.
AthleteOS builds the brick into your training plan by phase and weekly hours. It’s short and easy early, then race-pace in your peak weeks. When life happens, the AI coach decides whether to move, shorten, or drop the brick and tells you why. You can start a plan on AthleteOS and see where your first brick lands.
No study says you need a brick every week. A short one every 7-14 days, a longer one every fourth weekend, and honest recovery checks will get most athletes to the start line ready.