Whether it is Earl Woods teaching Tiger to form a mental image of the ball’s rolling into the hole, or Olympic weight-lifter Tara Nott’s training her brain to block out distractions, a strong mental game has always been part of elite sports. Michael Jordan, Nancy Kerrigan and Jack Nicklaus all practiced their moves mentally; Jean-Claude Killy used to ski a slalom course in his head umpteen times before exploding out of the starting gate. “Everybody is pretty much at the same level physically,” says American diver Michelle Davison. “[The difference comes down to] who can hold it together mentally.” That lesson has not been lost on the U.S. Olympic Committee. It had one full-time sports psychologist in 1988. Today it has five.

While coaches and trainers have long extolled the importance of the mental game, exactly how the mind affects the body’s performance has always been a bit of a mystery, with buzzwords like “in the zone” and “mental imagery” carrying a vague whiff of quackery. But just as physicians are showing that something as inchoate as a positive outlook can affect something as real as the progress of breast cancer, so scientists are uncovering how mental imagery and other tricks of the athlete’s trade affect the real, physical brain and hence the body. “Mental practice can actually increase real-world strength and performance,” says neuroscientist Ian Robertson of Trinity College Dublin, who describes the power of mental workouts in his engaging new book, “Mind Sculpture.” “Pumping virtual iron physically changes the brain–and the brain, after all, controls the body.”

The reason is that visualization activates many of the same neural circuits that actually seeing does. Imagine, in your mind’s eye, a harp in all its graceful detail; the same region of your visual cortex just turned on as if you actually looked at the instrument. But what matters to athletes is that, just as visual imagery activates the brain’s visual cortex, so imagining movement activates the motor cortex, notes Harvard University’s Stephen Kosslyn, who has done pioneering research on imagery. Imagine tensing and relaxing the muscles of your right index finger, but without actually moving. Were you to do this for several minutes every day for four weeks, at the end of the period the strength of that finger would increase by 20 percent or so, as researchers found in 1992 when they had volunteers follow this mental regimen. Nothing changed in the finger muscles themselves as a result of the imagery. Instead, connections between nerves and the muscles they control, in a circuit starting in the motor cortex of the brain, got stronger. “The improvements in strength were caused by changes in the brain,” says Robertson.

That’s probably why imaging is such a powerful, and popular, mental workout for athletes. “We try to get them to experience, in their minds, their ideal performance,” says USOC sports-psychology consultant Peter Haberl. That seems to be especially crucial in events requiring a series of precise movements, like long jumps, pole vaults or dives. Although scientists have not taken brain scans of a diver doing, say, a triple somersault with a twist, they have measured brain activity in people performing other complex movements. A 1995 study in Boston compared the brain regions of people who physically practiced a five-finger piano exercise with people who mentally practiced it. In both groups the area of the brain devoted to moving the fingers got bigger and accuracy improved. That same year, neuroscientists in London found that subjects who imagined moving a joystick activated pretty much the same areas of their brains as those who really moved it. The same process likely occurred in Backley’s brain as he mentally hurled the javelin. “Through mental practice, [he] kept stimulating the networks of connected neurons where his skill was embroidered,” Robertson writes. “By keeping these patterns of connections firing together… he preserved them.”

That’s what triathlete Nick Radkewich, 29, hopes will happen in his brain as a result of visualizing the cycling course. “I go over the course, where the hard turns are,” he says. “It’s almost like I’m looking through my own eyes, seeing the landmarks on the course, seeing the race occur.” Similarly, mental imagery may strengthen the neuronal circuits–millions of neurons firing in concert–that direct complicated moves like those in wrestling, and make them almost automatic. Lincoln McIlravy, 26, Team USA’s top wrestler at 152 pounds, has no doubt that overthinking your moves (especially in the heat of competition) can tie your brain in knots, so he relies on mental footage of his matches to make his moves automatic. “From the second the whistle blows, it’s all instinct. If you stopped the match, and asked me my name, I’d have to think about it. I never think ‘This would work or that would work.’ There have been times when I’ve thought, ‘An arm drag would work right now,’ but if it’s not automatic, it’s too late.”

Mental practice can be so real as to be exhausting. Diver Davison, 20, knows how that goes. At night she takes long walks, rehearsing each dive in her head. “I picture the perfect dive,” she says. “I’m actually tired afterward, from all the visualization.”

That undoubtedly reflects the intense concentration that mental practice requires. All the effects of mental workouts, from brain activations to finger strengthening, occur only if the imaging is accompanied by intense concentration. Attention matters. It can literally “sculpt brain activity by turning up or down the rate at which particular sets of synapses fire,” Robertson writes in his book. “And since we know that firing a set of synapses again and again makes the [neuronal circuit] grow bigger and stronger, it follows that attention is an important ingredient.” Attending to one sense also dampens activity in brain regions responsible for other senses, and perhaps for other actions. That’s why tuning out the crowd might improve performance: the brain may have more energy to attend to movement if it is not processing sound. Tara Nott is counting on it. When she steps up to the weight, she says, “I walk behind it and I stand there and I close my eyes. I just take a deep breath. I don’t see anything in front of me. I don’t see the judge. I don’t see the people in the stands. I can hear ‘C’mon, Tara!’ but it’s mostly a blur.”

Even the hoary notion that practice makes perfect has found a solid basis in neurobiology. As you progress in skill, “there’s less for you to consciously attend to or think about,” says sports psychologist and kinesiologist John Raglin of Indiana University. As a result the stroke, the swing or the jump becomes automatic. In fact, neuroscientists find that the more one practices a series of precise movements, the lower the brain activity often required to execute them. Let the mind games begin.