CHULA VISTA, Calif. — When Mike King raced BMX bicycles, the sport’s elite knew nothing of dynamic warm-ups, or core cooling, or thermal regulation. They did not mix sports drinks for maximum hydration and electrolyte balance.  They were BMX riders, and they resided at the intersection of counterculture and extreme sports, and the very idea of science as a means to improvement seemed downright uncool. This was before bicycle motocross became an Olympic discipline, before King became an Olympic coach, before his sport and its outdated training methods underwent a scientific revolution after its debut at the 2008 Summer Games in Beijing.  At a recent practice, King looked less like an employee of USA Cycling and more like the BMX pioneer he was in what now seems like another life. He wore a mesh hat cocked sideways and low-hanging shorts, his face covered in stubble, eyes hidden behind sunglasses.  King paused and considered how to answer a question about his team’s so-called magic pants and their powers of recovery.  “Magic pants?” King said as he grimaced slightly. “I really can’t discuss them.”  That Belichickian response showed how much BMX has evolved since the Beijing Games, transformed from rebellious adolescent into, King said, “something more grown-up.” As he spoke, the team’s video coordinator, wearing a hooded sweatshirt, recorded practice runs from a nearby roof, beaming the images and data to the iPads of coaches on the course.  One of those coaches, James Herrera, started in BMX in 1977. As he gravitated toward coaching, he focused on less developed training methods, returned to school and obtained master’s degrees in psychology and exercise physiology. Such methods sounded, at first, like a foreign language to his charges.  When King raced, advancements in strategy came mostly from watching competitors or reading textbooks. The basics: climb on small bike, pedal furiously, turn left, repeat. The riders traveled together, ate together and sometimes bunked together, a mix of French and British and Australian, with as much camaraderie as competition.  Some of the more serious athletes transitioned into other cycling disciplines. The British track cyclist Chris Hoy, winner of three gold medals in Beijing, started in BMX.  So did his teammate Jamie Staff, a gold medalist for Britain who became a track cycling coach for the United States. He used to watch Christophe Leveque, the Flying Frenchman, who dominated BMX throughout the 1990s with support from French sports federations. Staff and others were devoted, riding for six to eight hours daily. But that training, Staff said, was “misguided” and “uneducated.”  When the sport made the Olympic stage, other nations followed the Leveque model. BMX training became more like track cycling training, which had become more like road cycling training, with a process similar to the one used by Tour de France teams.  “It’s getting really scientific, which is not really BMX,” Staff said. “I know they’re trying to keep BMX cool and hip and trendy. At the same time, they’re changing the mentality. At this point, you buy into it. Or you don’t bother.”  When the 2008 Olympics rolled around, King concentrated on keeping his athletes relaxed. He knew the pressure and the magnitude would be higher than ever.  It felt, he said, like a culmination: BMX, at the highest level of sport, on prime-time international television; BMXers in the opening ceremony, clad in red, white and blue. This meant more money, more exposure, more legitimacy as a sport.  One future Olympian watched the event on television. His name is Connor Fields. He is a favorite for this summer’s London Games.  “The impact couldn’t have been bigger,” he said. “The Olympics justified and solidified everything we do.”  The minute the races in Beijing ended, another race began, and the United States program was caught flat-footed. The American men and women had seized half the Olympic BMX medals because they possessed the deepest talent pool, because the sport was created and incubated in Southern California.  That would no longer be enough, not after Australia, France and other countries put their considerable resources — more private financing and sports institutes — behind BMX in late 2008. The United States, Herrera said, fell “maybe a year behind.”  At the same time, King and company shifted their junior development strategy. They went for youth, replacing veterans with prospects, save for Mike Day, the elder statesman and a silver medalist in Beijing.  This article has been revised to reflect the following correction:  An earlier version of a picture caption with this article misstated the given name of a coach, James Herrera, as Mike.  An earlier version of a picture caption with this article misstated the given name of a coach, James Herrera, as Mike.
Bicycle motocross, once considered a counterculture sport, has undergone a scientific revolution since its debut in the 2008 Beijing Games.