A triathlon is not three sports. It is three sports and two joins, and the joins are where races are lost. You can be a strong cyclist and a decent runner and still spend the first two kilometres off the bike running like somebody who has never done it before. That feeling has a cause, and it has a cure, and the cure is boring and effective.
What a brick actually is
A brick is two disciplines back to back with as little gap as possible. In practice it almost always means bike, then run, because that is the transition that hurts. Swim to bike is uncomfortable. Bike to run is a different sport for the first ten minutes.
The point is not to get fitter. You will not get meaningfully fitter from the twenty minute run tacked onto your Sunday ride. The point is to rehearse a specific, unpleasant, entirely predictable experience until it stops being a surprise.
Why your legs feel like that
Three things are happening at once when you step off the bike.
- Your cadence is wrong. You have spent hours turning the pedals at a fixed rhythm with your hips at a fixed angle. Your nervous system has settled into that pattern and it takes a few minutes to let go of it.
- The muscles are loaded differently. Cycling is largely concentric work through the quads and glutes with your weight supported. Running is repeated impact with eccentric loading through the calves and hamstrings, taking your full weight. The same legs, a very different job.
- Blood is in the wrong place. It has been pooled in cycling musculature and needs to redistribute, and if you have been aero on the bars for four hours your posture needs to unfold too.
None of that is fixable. All of it is rehearsable, and the rehearsal shortens the window from roughly ten minutes to roughly three.
How to build one
Start smaller than you think, and change one variable at a time.
Level one: the habit brick
Any ride, any length, plus a ten minute easy jog immediately after. Shoes laid out before you leave. Off the bike, into the shoes, out the door in under three minutes. Do this once a week for a month and the strangeness starts to fade on its own.
Level two: the race-pace brick
Ride the last twenty to thirty minutes at your intended race effort, then run twenty to thirty minutes at your intended race pace. This is the one that teaches you what your real race pace is, which is nearly always slower than the pace you can hold on fresh legs.
Level three: the repeat brick
Alternating blocks, for example three rounds of fifteen minutes riding and ten minutes running. Brutal, very specific, and best used sparingly in the last six to eight weeks before a race.
The transition itself is a skill
Time lost in transition is the cheapest time you will ever save, because it costs no fitness at all. Practise the actual choreography, in your kit, in your driveway if you have to:
- Spin the last few minutes. Drop a gear or two and lift your cadence for the final three to five minutes of the ride. It pre-loosens the legs and costs you almost nothing.
- Unfold before you dismount. Stand up, stretch the back, get the blood moving.
- Elastic laces. Not optional. Bending down to tie laces on jelly legs with a heart rate of 150 is a small horror.
- Everything in one place, in order. Shoes, race belt, cap, gel. Same order every session, so on race day you are not thinking.
- Walk the first ten steps if you need to. Better than a stumble.
Start slower than feels right
The most common brick mistake is not the session, it is the first kilometre. Adrenaline plus fresh air plus relief at being off the bike produces a first kilometre well under target pace, and the bill arrives at kilometre eight.
Plan to run your first kilometre deliberately slow. Fifteen to twenty seconds slower than target is not timid, it is the difference between negative-splitting a marathon and walking the aid stations.
If your first kilometre off the bike feels comfortable, you have probably got it right. If it feels great, you are going too fast.
How often
Once a week is plenty in a build phase, and the run portion should stay short enough that it does not compromise the following day. A brick is a high-fatigue session dressed up as an easy one, and the extra pounding on already-tired legs is exactly where people pick up calf and Achilles trouble.
In peak weeks, one longer race-pace brick every ten to fourteen days, with the rest kept short. Then nothing heavy in the final two weeks. You are not building anything in the last fortnight. You are arriving.
The summary you can act on tomorrow
- Add ten easy minutes of running to one ride a week. That is the whole starting point.
- Rehearse the transition itself, in order, until it is automatic.
- Spin the last few minutes of every ride.
- Start the run slower than feels right, every single time.
Do that and the ten minutes that decide your race stop being a surprise and start being just another part of the day you have already practised.