Finishing first is a concept that is never far from her mind. For some athletes winning is a lubricant for life; for the 32-year-old it is the fuel that powers her relentless acquisition of titles and trophies. It was, after all, the naked pursuit of success which turned Grainger on to rowing at the age of 19. She had little interest in trying the sport, preferring outdoor pursuits like skiing or karate, at which she has a black belt, when a persuasive member of the rowing club at Edinburgh University's fresher's fair told her that she had the perfect physique to succeed at rowing. Grainger was hooked by the chance to feed the adrenaline-rush of success.

It is a long way from the cluttered confines of the Union Canal at Boroughmuir, where Grainger first tried out for Edinburgh University Rowing Club, to the purpose-built Shunyi Olympic rowing park in the shadow of Beijing International Airport, where the best rowers in the world will await her in a little under two months, yet her motivation today remains as unswerving as it was when she trained at Edinburgh and would envisage herself standing on the Olympic podium collecting her gold medal.

"I'm really proud of what I've achieved, of winning four world championships and Olympic silver medals (in Sydney and Athens]," she said, "but if I didn't get an Olympic gold (at Beijing] it'd be a profound disappointment because everyone knows it's what's missing from my trophy cabinet. Winning Olympic gold is the ultimate accolade. You're Olympic champion because you've beaten the best in the world at their peak. That's why the Olympics are unique."

This is Grainger's third Olympics, and although she says she won't make a decision on competing in 2012 until after Beijing, she knows this could be her last shot at the gold. Throw in the fact that the British four are widely tipped to win gold and it's surely a scenario that will pile pressure on her shoulders.

"There is always a danger that the pressure can get too much and the fear of losing can overwhelm you because obsessing about the prospect of failure can be paralysing," she says. "You've got to want to take on the challenge, to feel excitement rather than a sense of dread. You need to accept that nerves come with anything that you care about, and that by focusing on a positive outcome you increase your chances of success."

That is easier said than done – as the British crew demonstrated in two recent races. The first time Grainger's boat was edged out by the unheralded Chinese, no-one thought anything of it, dismissing it as an aberration. But when it happened in the next race too, with the British setting a punishing early pace to lead by over a boat's length at halfway only to see the Chinese reel them in and win comfortably, the alarm bells started ringing.

Grainger stresses that this will be a wide open Olympics, with reigning champions Germany and the Americans two of several crews able to challenge for gold. China, competing on home territory, are a huge threat. "China haven't been dominant in rowing, but since Beijing got the Olympics they've got stronger and stronger," she says. "We knew they'd be ones to watch, and they've been ratcheting up the intensity. It's never nice to be rowed down but we will be stronger for it because it's reminded us that we're not good enough to win an Olympic gold if we have a bad day.

"We weren't at our best. We were fatigued because we've been training so hard, and we weren't rowing very efficiently because there were a couple of technical things we were trying because these regattas are very much test events. But we've shown good base speed and proved that we can dominate the first half of races."

Were this any other sport then the issue of drugs would have raised its head by now. Rowing doesn't have a serious doping problem, but Chinese sport does. Even for someone with Grainger's look-on-the-bright-side optimism, her painful past experience when it comes to performance-enhanced opponents should provide pause for thought.

In the 2006 world championships at Dorney Reach in Berkshire, Grainger's quadruple scull was overtaken in the last 100m by the Russians. It was a devastating defeat and the sight of the four girls holding hands on the podium, close to tears, remains an enduring image of misery. Thrown into an introspective state of despair at their collective failure, the four oarswomen endured what the Scot calls a "very, very bleak winter".

It was almost four months later that they heard that Russia's Olga Samulenkova had tested positive for testosterone, which meant the disqualification of their boat and Grainger's elevation to gold medal. It was a hollow victory. "I still think of that race as one we lost, that was stolen from us," she says. The anger, though, did fuel a manic regime which transformed them into the formidable outfit that will race in Beijing.

Responding to extreme challenges that would sink less determined and self-assured athletes has become a familiar scenario for Grainger. When she won her first world championship gold in Milan in 2003, for instance, she injured her back so badly that three different specialists said her career was over. Grainger ignored them and carried on training. One day, miraculously, the pain disappeared.

She faced a similarly severe test of character when, after a disastrous fifth-place finish at the 2001 world championships, Cath Bishop told her she was calling it a day. Bishop changed her mind but British Rowing had her down as a flake and wouldn't let Grainger row with her, and told their coach he wasn't allowed to train them. So they trained in secret, travelling to Milan for the one race where they could book a place at the Athens Olympics by defeating the British pair. They did so, of course, coming second behind the all-conquering Romanians.

Grainger has an endearingly easy charm, but there are also unmistakable hints of a more obsessive side to her nature. After studying law she went on to do an MA in medical law and is currently doing a PhD in homicide. She has a fascination with the fanaticism that compels murderers to kill, but also knows that it is the dark flip side of the single-minded obsession that drives elite competitors to succeed.

"But it's not just about winning," she says. "I couldn't sacrifice the rest of my life just to win, but winning justifies everything I do – if I made the sacrifices and didn't have the vindication of winning, then this lifestyle just wouldn't be sustainable. Not for me at least."