Four years ago I made a commitment to run the London Marathon three times and raise £5m for children's causes through my trust.
And there was another good reason to swap road running for rowing too.
Steve lends a hand in 2003 after injury forced him to drop out
When I retired after the Sydney Olympics my coach wanted me to keep the training going and do a warm-down programme.
I wasn't interested in that. I had trained every day for 25 years of my life and once I'd retired that was it.
But I had always wanted to run the London Marathon. So I committed myself to the 2001 race and that gave me some motivation to complete my training.
I was going to run again in 2003 but I fell and broke my collarbone two weeks before the race so I wasn't allowed to take part.
I still had a great time at the marathon that year because I ended up holding the finishing tape when Paula Radcliffe smashed the world record. In the newspapers the next day you could see my hand holding the tape - another claim to fame!
It was always the long-term plan to run again in 2005. I had also set myself the target of breaking the world record for the most money raised by a single person in a marathon. The old record is £1.1m.
But after the tsunami disaster over Christmas I felt it was important to raise money for that instead. I've decided to run again in 2006 and I'll go for the record attempt then.
I started my training for this year's race in January and, even though I'm heavier than I was four years ago, I'm already in better shape than I was then.
I must admit I didn't prepare very well for my marathon debut. I ran a half marathon four weeks before the big day and that was the longest run I did leading up to it.
Running the race in 2001 was like doing the biggest lap of honour I could ever do
I was also the official starter that year, so after giving the green light to the elite runners I had to join in.
The experience was amazing. From a personal point of view it was like doing the biggest lap of honour you could ever do.
During the race so many people, including other runners, shook my hand, patted me on the back and said, "Well done for Sydney."
Afterwards my arms were more tired than my legs because I'd shaken so many hands.
A lot of people had told me when you finish the London Marathon you feel a real sense of achievement. I thought, you've got to be joking, after what I've achieved at the Olympics, I just won't feel that same sense of accomplishment.
But once I came down The Mall and crossed the line, I thought "yes, I've done it", and that's the special thing about the marathon.
The Steve Redgrave Trust raises money for the Association of Children's Hospices, the Children With Leukaemia charity, and the Trust's own inner-city schools project which aims to provide inner-city schools with rowing equipment.
This year Steve will donate all the proceeds from his London Marathon efforts to victims of the tsunami.
Steve will be writing a regular column on the ups and downs of his marathon training for the BBC Sport website.