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before bicycle motocross became an Olympic discipline, before King became an Olympic coach, before his sport and its outdated training methods underwent a scientific revolution after its debut in the 2008 Summer Games in Beijing.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, in 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, similar to the Tour de France teams and their sizable support staffs.

“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 Olympic event on television. His name is Connor Fields. He is a favorite in 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 U.S. 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 when Australia and France and other countries put their considerable resources — more private financing and sports institutes — behind BMX in late 2008. The U.S., 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.

The U.S. retained the sport’s largest talent pool but needed to take a more scientific approach to training. Herrera was mindful of the pattern in another cycling discipline. Mountain biking, he said, was also created in the U.S., and yet an American last won an Olympic medal in that sport in 1996, its first year in the Games.

The U.S. BMX program underwent a training overhaul. Herrera came onboard. Simple dietary changes were instituted: no dessert or sugary energy drinks; more fruits and vegetables and nutritional supplements. Jerseys were designed to be tighter and more wind-resistant.

Coaches studied different exercises in the gym and measured their effects on the bike. They added power meters, as in the other cycling disciplines, and based on the data they accrued, they adjusted the volume of on-course training and its frequency, determined whether riders needed more practice on uphill or downhill sections, and selected gear.

They hired a videographer who used the computer program Dartfish to show riders the best lines to take on a given turn. Video of individual riders could be placed side by side on a screen, as if they were racing, to compare which one took the most direct route.

In most elite BMX races, Herrera said, the winner finishes less than 1.5 seconds ahead of the competitor who finishes 64th. Often, the gap is less than one second.

“In my era, we’d probably roll our eyes,” King said. “But at this level, with the money we spend, 1 percent of improvement based on sports technology could be one-thousandth of a second, which could be the difference between a gold and silver medal.”

Before the 2008 Games, the U.S. built a replica of the Beijing course at the Olympic Training Center here. Each year, it hosted an official race. Day won the first one in 35.9 seconds. Fields won the most recent one in 33.6, a difference, he said, of 10 to 20 meters.

Those gains, which Herrera described as massive and astronomical, came in large part because Fields, 19, emerged during BMX’s scientific revolution. His coach, Sean Dwight, said BMX, with athletes on tiny bikes that travel down steep ramps in three seconds at 40 miles an hour with seven other competitors to contend with, is more explosive than the 100-meter dash and as explosive as weight lifting.

Dwight focuses most on Fields’ biomechanics, believing that an ideal position on the bike produces maximum power. He knows almost immediately whether Fields’ head is tilted two inches the wrong way, or his shoulders are too far back.

While Fields helped push BMX into this new territory, the courses grew longer, the jumps higher, the turns more dangerous. If this made BMX more viewer-friendly, it also worried coaches.

The replica London course sits near the replica Beijing course, and it appears at least twice the size and twice as difficult. The first jump, Herrera said, is the length of three to three and a half cars. King said BMX had “reached its threshold,” just as he said four years ago. Asked if the progression meant somebody could ultimately die, he said, “I hope not.”

Regardless, the scientific revolution will continue. King said riders were once ridiculed for acknowledging that they took ice baths. He laughed and called the progress mind-boggling and added, “You know, it’s still a bike race.”

He won plenty of those without science, but the U.S. achieved no gold medals in Beijing, which was the program’s goal. If that meant that BMX had to lose some of its counterculture cool, well, consider King a convert, magic pants and all.

© 2012 The New York Times Company