A self-proclaimed expert's treatise on personal aerodynamics for the cyclist
Aerobars basically put you in superman position on the bike: arms projected forward and together - over the front wheel, back flat and basically parallel with the top tube, ass back on the seat. All this achieves a number of effects.
First, it brings together the hands, which brings together the arms, closing the airdam of the chest and doming the upper back.
The decreased frontal profile lowers wind resistance because of a smaller frontal cross-section. The domed and flattened back makes the flow of air more laminar again lowering drag.
Once you get a cyclocomputer mounted on your bike, the gains of good profiling on the bike, aided by aerobars in particular, are very obvious. Try this simple test! Start out with a steady cadence in a relatively high gear, with a good straight stretch of road. Have your hands spread on the handlebars, with your body erect. Your basic "riding your bike to class" posture. For me, this gives an indicated ground speed of around 17mph.
Let's get to the profiling. If you're on a road bike, get down in the drops (the lower level of the bars). If you're on a mountain bike, just get low over the top tube and headset. For me, this instantly brings my speed up to 19mph. I just gained a "free" 2 mph, just by changing how I posture myself on the bike.
It's time to start cooking with gas. Get down in the aerobars. The first time you do this, you will feel like you are going to crash the bike. This is because you have moved your center of gravity from its comfortable home over the crank to somewhere near the front wheel. Your steering is now going to get hyper-responsive. You will also make note of the fact that you can't operate the brakes. Aerobars are not for the faint of heart. Take a look at your speedometer. For me, I pick up another 2 mph - same effort, 21 miles an hour.
As far as getting into and out of aero position, try going one arm at a time, head up, moving slowly to keep your track and balance. You'll habituate the move in time, and not feel like you're taking your life in your hands every time you do it. But the benefits are big. Free speed, another position for those long century rides. And you look like a badass.