Usain Bolt made the sign of the cross, pointed to the heavens, and kissed his skinny fingertips. Two lanes over stood Justin Gatlin, his thick shoulders filling out his bright-red team USA tank top, diamond studs in his ears. He was as somber and focused as Bolt was loose. The runners set their feet in their respective blocks and placed their fingers on the track, waiting for the gun.

Like Bolt, Gatlin had tasted Olympic glory before, having won gold at the 2004 games. But that was a lifetime ago—before a ruinous 2006 doping ban, before authorities annulled his world record and exiled him from the sport for four years, and before the 2008 Summer Olympics when Bolt burst onto the scene, running the 100-meter dash in an unthinkable 9.69 seconds, leaving the entire field behind him and erasing any thought of Gatlin.

It had been a long road back. Gatlin settled for the bronze in the 2012 London games as Bolt broke his own world record with a blistering 9.63. But the distance was closing. As Bolt and Gatlin crouched over that starting line at the 100-meter finals of the 2015 World Championships in Beijing, one announcer called the matchup a "world heavyweight title boxing match." In the semifinals, Gatlin pulled off a performance so flawless many thought the 100-meter final was his to lose.

At the pop of the starting gun, Gatlin exploded off the blocks. Bolt had a slight edge in the straightaway. There were nine men in the race, but the two rivals surged ahead, hurtling toward the finish line, heads extended. They finished so close that when it was over you needed high-speed photography to have any chance of understanding what happened: Bolt won the race by ten milliseconds. One-tenth of an eyeblink. Four inches.

This August, at the Rio Olympics, will be the first time the two men race again. In the rarefied air world-class sprinters breathe, it takes about forty-six strides to get from the starting blocks to the finish line of the hundred meters. If Gatlin can knock just two ten-thousandths of a second off each stride—and Bolt hasn't improved his pace—he'll take the gold.

Four high-speed cameras record Gatlin's starts. Peter Bohler

Those two ten-thousandths of a second are why Ralph Mann, USA Track & Field biomechanist for sprints and hurdles, has set up a computer monitor and a laptop on a flimsy folding table next to the track in Orlando where Gatlin and his coach are practicing on a hazy spring Tuesday. From Mann's table wires snake outward across the red rubberized track and connect to four high-speed Casio cameras capable of recording three hundred frames a second, fast enough to capture the individual beats of a hummingbird's wings. The cameras are arrayed around Gatlin as he digs his heels in against a pair of force-sensing starting blocks. He places his fingers on the ground to set his stance and waits for his cue.

"Ready!" his coach yells. "Set … Go!"

At thirty-four, Gatlin is an old man in the sport. Yet he's never been better. He launches himself off the blocks, his upper body virtually parallel to the ground, his arms a blur, his feet tapping the track like fingers drumming a tabletop. At the three-meter mark, Gatlin pulls up and ambles over to Mann's table. Mann rewinds the video and superimposes a stick figure composed of lines in different fluorescent hues directly over Gatlin's tattooed, muscular frame on the screens.

The positions of the stick figure represent Gatlin's "ideal" body positions, a perfection of angles and form optimized at each point in time and space for efficiency of motion. If Gatlin can match each click of the figure's movement, if sprinter and stick figure can run in lockstep on that screen, Gatlin won't just put Bolt away, he'll shatter world records.

"That's half a tenth of a second faster than anybody else on the planet. That's how good that start is."

Mann taps a button and Gatlin's start unfolds in slow motion. At this pace, the horizontal tilt of Gatlin's trunk is a marvel—low and level to the ground, he'd surely face-plant were it not for the power and impossible frequency with which he propels his feet into the track. After months of work, there's not much daylight left on Mann's screen between the stick figure avatar and the real thing. Offset clicks are rare.

"This is what you do better than anybody else," Mann says, pointing to Gatlin's outstretched form, his torso even lower than the target line. "Right there. You should travel with me a little while to see how tough it is to do that."

Suddenly, a single fluorescent line representing the ideal position of Gatlin's left leg inches ahead of his actual body on the screen. His back leg has stalled ever so slightly.

"That's one click behind the model," Mann says, freezing the video at the end. "One! That's beautiful. Holy Jesus. That's half a tenth of a second faster than anybody else on the planet. That's how good that start is."

Mann pauses just long enough to allow Gatlin to absorb the reality.

"You got one more start in you?"

If anyone can find a way to shave off the two ten-thousandths of a second that separates Gatlin from Bolt, Mann is the one to do it. For more than three decades, Mann has used technology to make people faster. He is a biomechanist. He built the statistics-based computer program he calls his "performance model" by filming hundreds of world-class sprinters competing at track and field events around the globe. Then he extracted a dizzying array of variables from each performance—everything from the lengths of each runner's feet, ankles, and forearms to the angles and precise location these body parts occupy in relationship to one another and the track at any given second of a race.

"Ralph gives me times that I need to hit for a certain part of the race. He says, 'This time right here will put you at 9.7 to 9.6 pace,' " Gatlin says, "and he's always been correct. Each time when he comes before the season and I hit a certain time that he said 'This is where you'll be at,' that's where I'm at. So I put my trust in him."

Peter Bohler

Mann's obsession with the biomechanics of speed predates his interest in science. At sixty-seven, Mann is long and lean and moves with the grace and confidence of a natural athlete. He runs, bikes, lifts, and skis. Were it not for his snow-colored hair, he could pass for a much younger man.

The son of a former semipro baseball player who worked the docks of Long Beach, Mann was groomed early on for glory on the baseball diamond, and earned a scholarship from the University of Southern California. He turned it down for a track scholarship to Brigham Young University, where he specialized in intermediate hurdling.

"Damn near broke my dad's heart," Mann says.

Back then, Mann recalls, the knowledge of sprint mechanics was practically nonexistent.

"The understanding of what it took to be fast was totally unknown," he says. "We had no idea. You just ran."

Mann broke a U.S. hurdling record and claimed NCAA glory for the BYU track team. At the 1972 Munich Olympics, Mann roomed with Bruce Jenner and a crazy shot-putter named Brian Oldfield, who was known for psyching out opponents by smoking cigarettes between throws, and who later posed for Playgirl. In the 400-meter hurdles, Mann took home a silver medal, defeated by an inconsistent Ugandan who ran the race of his life.

After the games, Mann went on to pursue a doctorate in biomechanics at Washington State University, where he began building a mathematical depiction of speed, initially picking apart the biomechanics of the long jump. The model would serve as the basis for both his dissertation and the athletic consulting firm he opened after he realized, about eight years into an academic career, that standing on the edge of a track was more fun than standing at the front of a lecture hall.

His involvement with USA Track & Field dates back to the early 1980s, a time, Mann recalls, when "we were just getting killed by the East Germans and the Russians." Systemic doping was certainly part of the reason. But it was only one part of a larger effort.

"They had a great biomechanics program," Mann says. "They set it up and they produced incredible athletes, and basically we did nothing. We sort of came out and said, 'Okay, run faster. Lift your legs, pump your arms,' and that wasn't working."

Mann volunteered to analyze sprinters and hurdlers and spent the next ten years refining his models, working off and on with the organization and leading track and field coaches. Then, six years ago, USA Track & Field hired Mann and his firm to provide regular analysis to all of the top U.S. sprinters and their coaches as part of a new sports science initiative.

That was 2010—a year, as it happened, when there were few people who had more reason to listen to Mann than Justin Gatlin. That year the elite sprinter finished his doping ban. When Gatlin came back from what Mann calls his "drug vacation," Mann recalls, "he was awful."

But it didn't stay that way for long. Gatlin set out to recapture Olympic gold—this time using science to help him.

When he was a kid growing up in Brooklyn, Justin Gatlin hurdled the fire hydrants lining the streets outside his home near Sheepshead Bay. By the time he was in high school, his family had relocated to Pensacola, Florida, where Gatlin's acrobatics won him a full ride to the University of Tennessee as a 110-meter hurdler. Gatlin's coaches at Tennessee switched him to sprinting, and he flourished. In just two years, Gatlin won six consecutive NCAA titles, and in 2002, he turned pro. At twenty-two, in the 2004 Athens Olympics, Gatlin sprinted to a gold medal in the 100 meters, clocking a blazing 9.85 seconds. He was the fastest man in the world.

"It was surreal," he recalls. "It's just a whole different kind of feeling, coming across the line. A hundred thousand people in the stands watching you, crowd roaring, going crazy. It's the one moment where everyone in the world stops."

Gatlin has gone from a below-average starter to the best Mann has ever seen. But he still has work to do.

Two years later, Gatlin reached another high, when he equaled the world record of 9.77 in Qatar. Then it all came crashing down. That July, Gatlin revealed he had tested positive for performance-enhancing drugs. Testosterone. In the pantheon of doping excuses, he holds a world record for absurdity: He accused a vengeful massage therapist of sabotaging his career by surreptitiously applying an illegal cream. Not that anyone was really listening. Gatlin's coach at the time, Trevor Graham, soon had eight of his athletes ensnared in doping scandals. He would later receive a lifetime ban from the sport.

Gatlin's world record was erased. He served out his ban as Bolt ascended, and, at Gatlin's first race back in 2010, he was shaky off the blocks—"like a car that is starting really fast and fishtailing," according to his then coach. His time, 10.17, was a world away from Bolt. It seemed as if he was finished. But Mann had already begun evaluating the sprinter and had diagnosed his weaknesses. Gatlin was leading with his trunk, leaning too far forward. There were problems with the way he positioned his legs. His nervous system wasn't yet primed to produce explosive power. And there was an even bigger problem. Gatlin was fat.

"Weighing 210 pounds wasn't going to get the job done," Gatlin recalls Mann telling him.

In 2012, Gatlin signed with a new coach, Dennis Mitchell, a retired three-time former Olympian, and things began to turn around. His coach introduced a new structure and consistency into Gatlin's training regime, managing his diet and designing a new circuit-based weight-room routine. Gatlin dropped to 175 pounds. His body fat percentage fell from twenty-five to just six.

On the track, the coach set about fundamentally redesigning Gatlin's gait based on insights that came out of Mann's models.

Speed is simple, Mann likes to say. There are primarily two components: the number of strides a runner takes each second and the length of those strides. Each comes at the expense of the other, and a coach has to decide which to emphasize. That's where Mann's performance model comes in. Its algorithms are calibrated to produce the maximally efficient ratio, based on body type and a whole host of other variables, including race length, the length of different limbs in relation to one another, and overall height and weight.

One of the clearest insights to emerge from Mann's models is one of the most important for Gatlin if he is to triumph over Bolt in Rio: It is far more effective to strike the ground with your foot out in front of your body—and focus on immediately getting that foot back up in the air—than it is to push off with a foot that is behind it. Both the angle of impact and the position of the different muscles in relation to the ground with the foot out front, Mann argues, generate as much as 20 percent more force. That extra force is essential for achieving the ideal tradeoff between foot touches and stride length. If you want to maximize foot touches, you have to get off the ground quickly, and the only way to get off the ground quickly, while maximizing force, is by hitting the track with your foot in front of you, Mann says.

Mitchell had embraced this reasoning by the time he started working with Gatlin, and he quickly recognized they had a problem.

"He was a very powerful runner, so his stride was very elongated and powerful," Mitchell says. "We took at least two years to try to shorten that up. He was a push-off guy, and I changed him to a strike guy. We changed his technique up totally."

Mann's models suggested that Gatlin's start needed major modification. Rather than catapult forward off the blocks with long strides, Mann's models suggest that it is as much as 30 percent more efficient to take smaller steps that sacrifice raw power for quantity. The model shows that it maximizes opportunities to push off the ground, which are essential for initial acceleration. But Gatlin's tendency was to explode out of the blocks with long strides, wasting valuable time in the air.

"Justin was a good, powerful runner, he had run fast," Mitchell recalls. But he added that Justin's start was still technically flawed.

ustin Gatlin of the United States celebrates after crossing the finish line to win silver in the Men's 200 meters final during day six of the 15th IAAF World Athletics Championships Beijing 2015 Andy Lyons Getty Images

Mitchell designed a program aimed at creating new muscle memory in Gatlin. He'd practice his start and his strides tethered to bungee cords or sleds weighted down with fifty pounds. The resistance slowed the motion of the start, allowing Gatlin to exert the same explosive force while making it possible for Mitchell to tweak Gatlin's biomechanics and for Gatlin to connect the new concepts of the mind to the feelings in his body.

Over the last two years, Gatlin has gone from a below-average starter to the best Mann has ever seen. But he still has work to do. Mann's models show that Gatlin has a tendency to let his hips come forward ever so slightly, subtly shifting the angle at which his feet strike the ground. The tendency costs him just the tiniest slice of time—but it could make all the difference against Bolt.

Gatlin, Mitchell, and Mann all know the solution is practice. At the track in Orlando, rising from his chair at Mann's track-side table, Gatlin resolves to regain that one "click" that put him behind his virtual avatar on his start. Doing so will require Gatlin to consciously yank his left leg forward with more power after coming off the blocks.

Gatlin takes his position on the track, Mitchell behind him. Mann is ready to film.

"Ready," Mitchell yells. "Set … Go!"

This time, when Mann cues the footage, the time tells the story. Gatlin is two hundredths of a second faster than his previous trial, dropping below a 0.7- second start for the first time ever—breaking the record for the fastest start Mann has ever clocked.

"Every click is gold," Mann says. Then Gatlin walks back to the starting line, sets his feet in the blocks, and goes again.

*This article origionally appeared in the July/August issue of Popular Mechanics.

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