Brick workouts suck. Plain and simple. I hate them. I also love them. They are a very important part of training that I often neglect to do until the week before a race. Alot of people argue if brick workouts actually do any good, I think they do, I just hate to do them. Let me explain.
A "brick workout simply refers to training in two or more disciplines during the same workout, one right after the other with minimal or no rest in between, so basically it is race condition training. Most people, when they speak of brick workouts, usually refer to a bike/run brick, although it could also be a swim/bike workout.
I practice the bike/run brick the most because that is the toughest transition for me. Biking and running are totally different. Basically after coming off the bike and transitioning to running, your legs feel really heavy (which is why they call them bricks). The reasoning is that the heart rate goes up during the run and the heart is working to pump blood to muscles used for running instead of biking. It usually takes me almost a mile to get into my running legs and if I really push it on the bike, I always seem to deal with calf cramps coming off the bike. So brick workouts are designed to shorten the time for you to get your running legs.
Typical brick workout for a Sprint Tri:
Bike 5-6 mile, then run 1 mile, repeat 3 or 4 times! See now why they suck??? Starting out you should probably tone it down some and work your way up. If I would do more of these workouts, I think I would have so much better times.
So do they work?? Guess it depends on the person. For me it is more of a mental workout than anything. It is about busting through that wall of first wanting to quit and walk. Once you walk the first time, it is that much easier to walk the second time and third time, etc... So I think they are a valid workout, just wish I did more of them throughout the year!