How to fuel a brick session
How should you fuel a brick? Plan it by the total time of the whole session, not leg by leg, and do most of your eating on the bike, where your gut copes best. Then take a smaller amount on the run. A two-hour brick needs the same fuel as a two-hour ride, just arranged so the run doesn't get the worst of it.
Most triathletes and duathletes treat bricks as a run test after a bike. I think the bigger value is as a fuelling test. A long brick is the only session in a normal week that looks like race day from the stomach's point of view, and most people waste it by eating whatever's in the cupboard.
Plan for the total time
The guidance from the American College of Sports Medicine sets carbohydrate by how long you're exercising. A brick is one session, so add the legs together.
| Brick | Total time | Carbs per hour | Where to take it |
|---|---|---|---|
| Short: 45 to 60 min bike, 10 to 15 min run | Under about 75 min | Little or none, a carb drink or mouth rinse is plenty | A bottle on the bike, nothing on the run |
| Standard: 90 min bike, 20 to 30 min run | About 2 hours | 30 to 60g | Most of it on the bike, a gel or a few sips on the run |
| Long: 3 hours bike, 45 to 60 min run | About 4 hours | Up to 90g if your gut is trained | Steady on the bike, smaller and frequent on the run |
| Swim, bike, run race rehearsal | 2 to 5 hours | Match your race plan | Breakfast covers the swim, then race products on the bike and run |
For sessions of 45 to 75 minutes, the same guidance says small amounts of carbohydrate, even a mouth rinse, are enough. Between one and two and a half hours, 30 to 60g an hour. Longer than about two and a half hours, up to 90g an hour, using a mix of glucose and fructose so your gut can absorb it.
Notice that most of the short bricks people do in midweek training barely need fuel at all. A bottle of carb drink on the bike is fine. The serious planning is for the long weekend bricks.
Why the bike does the heavy lifting
Your gut handles food better on the bike than on the run. A review of gut complaints during exercise found that 30 to 50% of athletes report them. Severe gut problems were rare in marathon running and cycling, around 4%, but reached about 32% in Ironman races. Ironman is the event that looks most like a long brick: hours of eating on the bike, then a run.
So in a brick, as in a race, the bike is your kitchen. Front-load the session:
Start eating early on the bike. Within the first 20 to 30 minutes, not when you start to feel it.
Keep it steady. Small amounts every 15 to 20 minutes are far easier on the gut than a big feed every hour.
Ease off in the last 15 minutes of the ride. Don't stuff down a bar right before you rack the bike and start running.
On the run, go smaller and more often. A gel with water every 20 to 30 minutes, or sips of carb drink, rather than anything you have to chew.
If your hourly target on the bike is 70g, it's normal for the run to sit lower. Runners can take less than cyclists of the same fitness, and that doesn't change because you've just been on a bike.
Use the long brick as a dress rehearsal
This is the part most people skip, and it's the bit that pays off.
Your gut adapts to what you feed it. In one study, cyclists and triathletes who trained for 28 days on a high-carbohydrate diet with carbs during sessions burned more of the carbohydrate they drank during exercise afterwards: about 64g against 55g before, in a 100-minute ride. The group who trained on lower carbs didn't change. It's one study and it wasn't a gut training protocol as such, but it fits with what every experienced triathlete knows: if you only take race-day amounts on race day, your stomach won't be ready.
So on your long bricks:
Use your race products. The same drink, the same gels, the same bars. If the race hands out a particular drink on the run, train with it.
Hit your race numbers. If your plan is 80g an hour on the bike and 50g on the run, practise exactly that.
Ride and run at race effort for part of it. Fuel that sits fine at easy pace can turn on you at race pace.
Keep a note. What you took, when, and how it sat. Two or three bricks will tell you more than any article.
Build up. If you're nowhere near your race numbers, add 10 to 15g an hour every couple of weeks. Our gut training guide covers how.
Drinking and salt in a brick
Drink to your sweat rate on the bike, and carry something on the run if it's longer than about 20 minutes. If you dry with white salt marks on your kit, plan some sodium into your bike bottles. Our guides on sweat rate and salty sweaters cover how much.
Don't overdo it either. Drinking more than you sweat over a long session is how people end up with low blood sodium, and a brick in the heat is a classic place for it.
Swim, bike and duathlon bricks
Not every brick is bike then run.
Swim to bike. You can't eat much in the water, so the swim is fuelled by what you ate before. Start eating on the bike soon after you're settled, the same as you will in a race. Our open water swim guide covers long swims.
Run, bike, run. Duathletes face the hardest version: running first, then eating on the bike, then running again. Eat early on the bike while your stomach settles, and keep the second run light.
Full race rehearsals. A few weeks out from a middle or long distance race, a swim, bike and run rehearsal is the best test of your whole plan, including breakfast. Our triathlon fuelling guide covers race day itself.
After the brick
Eat a normal meal with carbs and protein once you're done, especially if there's another session the next day. You don't need anything special. Our recovery window guide covers timing.
FAQ
Do I need to eat during a short brick? Under about 75 minutes, not really. A carb drink on the bike is plenty, and many athletes take nothing.
How many carbs per hour on a long brick? Up to 90g an hour on bricks of more than about two and a half hours, if your gut is trained for it. Most of it on the bike, less on the run.
Why does my stomach turn on the run after the bike? Usually too much, too late on the bike, or too much in one go. Eat earlier and in smaller amounts, and ease off in the last 15 minutes of the ride.
Should a brick be fuelled like race day? The long ones, yes. That's their biggest value. Short midweek bricks can stay simple.
Sources
Thomas DT, Erdman KA, Burke LM (2016). American College of Sports Medicine joint position statement: Nutrition and athletic performance. Medicine and Science in Sports and Exercise 48(3):543-568.
Jeukendrup A (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine 44(Suppl 1):S25-S33.
de Oliveira EP, Burini RC, Jeukendrup A (2014). Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Medicine 44(Suppl 1):S79-S85.
Cox GR et al. (2010). Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. Journal of Applied Physiology 109:126-134.
In MOVE a brick gets its own carbs per hour for each leg, worked out from that leg's sport, length and effort, with the run leg kept lower than the bike. You can set fluid and sodium per hour on each leg too, so your long bricks run on the same numbers you'll use on race day.
Put this into practice
MOVE applies these principles automatically, personalised to your sport, weight and training load.
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