Brick runs are probably the most misunderstood session in triathlon. People think they're about running fast off the bike. They're not, not really. They're about teaching your body that running straight after cycling is just normal, not some kind of emergency.
First reason I actually love them - you come off the bike already pumped. Heart rate's up, adrenaline's there, you're ready to go before you've even started. Most sessions you build into. This one you're already at it.
Second reason: it teaches your body to switch. Cycling and running use your legs completely differently - different muscle recruitment, different movement pattern. First few times, it just feels like jelly legs. Brick runs train that transition, over and over, until it stops feeling like an emergency and starts feeling normal.
And third - for a few minutes, it just feels like race day. Legs still spinning from the bike, straight into finding run legs under real fatigue, chasing a number instead of easing into it. That's the closest simulation of race morning I get outside of an actual race. Like I'm flying. That feeling's addictive.
