"[Hutchison] took that and modified the breaststroke kick of all his elite athletes," says Wei, who presented his work to USA Swimming, the sport's governing body, in 2007. In a sport in which shaving tenths of a second can be cause for celebration, Hutchison reported that by adapting her kick, Kukors dropped several seconds in a breaststroke event, although she just missed the Olympic team. Jendrick and another of Hutchison's swimmers, Margaret Hoelzer, are competing this week at the games, where Jendrick placed fifth in the 100-meter breaststroke and Hoelzer, who won a bronze in the 100-meter backstroke, hopes to win gold in the 200 back. She broke the world record in the event in July.

More recently, Wei has turned his attention to a swimmer's thrust. With funding from USA Swimming, Wei built a force balance, an upside-down triangular frame that acts like a bathroom scale. Swimmers lie outstretched in the water and kick into the frame, and it measures their propulsion over time. The output, which for an elite swimmer like Kukors showed a sinusoidal, repetitive wave, can help coaches determine whether an athlete should try to generate more force with a harder, bigger kick rather than a shallower, quicker one. "It depends on the individual swimmer," says Wei, who hopes to combine flow and thrust measuring tools into one image. He also wants to make more measurements of athletes swimming freely, rather than pushing against a wall or in a flume.

Wei will meet with USA Swimming biomechanics coordinator Russell Mark in the fall to talk about what to do next. "Russell's job is providing coaches with a sound physics base for whatever they tell swimmers to do," Wei says. USA Swimming also relies on computer-based flow analysis using whole-body scans of swimmers; these could be combined to determine how one validates the other.