How to be champion in swimming.

"Take your marks." The swimmers bend down on their blocks, ready. The buzzer sounds. Eight of the best male freestyle swimmers in the United States dive into the pool. In a little under 2 minutes the200-meter Olympic swimming trial semifinal is over, and two swimmers are headed to the 2012 London Olympics.

Those swimmers are Michael Phelps and Ryan Lochte, two men with arguably the best freestyle form in the world. But why did Lochte beat out Phelps in this particular heat? New research being published in the Journal of Biomechanical Engineering may not answer that question, but it does lend a bit of scientific credence to their strokes. The short version: It's all in the arms.

Rajat Mittal is a mechanical engineer at Johns Hopkins University and lead researcher on a project to study the fastest swimming technique. Mittal says swimmers used two different kinds of arm strokes when training for and competing in freestyle events.

One, deep catch, is about as simple as swimming gets. When your arm enters the water, you try to pull it straight back exerting as much force as possible. It's a difficult stroke to master. Even the highest-level athletes need to change up their strokes on long-distance swims because of the sheer strength it takes to propel through the water with a straight arm.

The other stroke, sculling, became popular in the 1960s when a prominent coach encouraged his athletes to move their arms like propellers underwater. Instead of trying to move yourself through the water using only your shoulders, the sculling stroke allows a swimmer's elbows to jut out slightly, making it easier for the hands to wave through the water like a propeller creating less resistance.

Mittal's research focused on one seemingly simple question: Scientifically, which stroke should propel swimmers the fastest? The team started with video; USA Swimming provided Mittal and his team with underwater tapes of world-class swimmers using both the deep catch and sculling strokes while swimming laps. Mittal also modeled the arms of a few swimmers to use in computer animations of the strokes, a time-consuming process.