World champion lightweight sculler Duncan Grant can't complain about lack of variety in his opposition as he prepares to defend his title for the fourth time in as many years.

A high achiever with a low profile, there is little chance the Wairau oarsman will be taking another title for granted when the world rowing championships begin at Lake Karapiro on Sunday.

The nature of his specialist event means he has to contend with a never-ending procession of ever-changing opposition, his only defence coming from meticulous preparation and the hard grind of training.

"In my event, the numbers change every year," Grant told NZPA. "My event's the non-Olympic event - people change boats, crews break down from the doubles and fours, people decide they want to do something different for a year, so they end up coming to do the single.

"My field every year pretty much is different people coming in."

Grant contested the final two World Cup regattas in Munich and Lucerne earlier this year, returning with a second and a fifth placing.

The races in Munich and Lucerne were won by Hungarian Peter Galambos, while Briton Zac Purchase - teaming up with Mark Hunter in the lightweight doubles at Karapiro - took the first World Cup event in Bled, Slovenia.

The World Cup series saw rowers from Greece, Japan and Brazil in the lightweight sculls, as well as the more traditional rowing strongholds such as Hungary, Great Britain and Norway.

Opposition can surface from unexpected directions: "Last year I raced a guy from Greece, then there was someone from Denmark who'd been in lightweight doubles and come second and third at the Olympics. You sometimes get countries like Iran in there too."

The reason behind the somewhat transient nature of lightweight sculls - lightweight being under 70kg - lies with the fact that the event isn't on the Olympic calendar. Doubles and fours, yes. But not singles.

So although Grant has proven himself time and again at an elite level, the lure of an Olympic gold medal is still tantalising him. Hopes of pressing for a place in the lightweight doubles at the 2008 Beijing Games were thwarted when an ill-timed run with injury kept him off the water for two months in the all-important summer preparation phase

"I was out with compression syndrome in my forearms - you lose sensation in your hands and your forearms swell up so you can't hold the oar. Then I strained my pectoral muscle, the bicep, in cross-training," Grant remembers.

Finally back in the boat in January 2008, Grant was then hit with tendonitis at the back of the knee, more time off training, and the realisation that his Olympic dream would have to be put on hold for another four years.

"My one rowing goal I still have to achieve is to make the Olympics. The reason I'm in singles this year is because of the world championships," he said. "If it wasn't for that, I probably would have looked at moving up this year.

"You need time to build up a boat, especially in the lightweight grades, which are highly competitive."

With a promising crop of younger lightweight rowers coming through, Grant is hopeful of being able to build up a medal-winning combination either in the doubles or fours "selectors dependent, of course".

But although the 2012 London Olympics are still a major long-term goal, Grant has had no difficulty in maintaining motivation ahead of the first world championships on New Zealand waters since 1978. His No 1 world ranking is, he admits, a jealously guarded commodity.

"I'm always out to win - I wouldn't be here otherwise. In every sport, if you're the top of the pile, you're the target one everyone wants to knock off."

Grant's run in into his fourth title defence hasn't been ideal, with tendonitis in the knee necessitating a series of cortisone injections and forcing him off the water for three or four weeks after returning from the World Cup regattas in July.

Back in the boat in late August, Grant has been working hard to regain the form that has made him the rower to beat for the last three years.

"Obviously it doesn't make it any easier if you are at the top, you've got to keep working harder and harder trying to stay ahead. It's that striving for perfection - nobody can be perfect, but you try to be as good as you can."