The 29-year-old doctor, whose Beijing triumph was the only gold medal won by a Tasmanian since 2004, said after the injury-ravaged campaign he endured with long-time double scull crewmate Dave Crawshay, it didn't take long to commit the next four years of his life and the chance of a fourth Olympics.

In fact it took 10 days, Brennan making the decision as he stood in the middle of the Olympic Stadium on August 12.

``I had inklings leading up to London that I would like to keep going to Rio but the closing ceremony was when I really knew,'' he told The Examiner yesterday.

``After our race I was too upset to think about it but as they were extinguishing the flame I was pretty much set.

``There's a few moments at the Olympics that are really important and one of those is extinguishing the flame because it brings an end to the four years of effort I've just put in. It's quite an emotional moment and for me there was a feeling of loss and disappointment.''

Brennan, who rows with Lindisfarne but is based in Canberra, said he drew on his success in bouncing back from disappointment at his first Games in Athens, where he came seventh in the quad scull, to win the double four years later in Beijing.

``The moment in London had the familiarity of what I experienced in Athens. I guess I'm a lucky person that I can relate this experience to one I've had in the past when I did come back and achieve what I wanted to.

``But what London taught me was quite how fortunate we were that we did not have any injuries in the lead-up to Beijing.

``It made me realise even more that you have to have a smooth run and now my goal for the next four years is not to get injured.''

Brennan said his closing ceremony realisation was in contrast to the emotions he endured as he and Crawshay watched the Olympic final at Eton Dorney without being in it.

Six weeks of lower back injuries preceded the Games with Crawshay forced out of the boat for the Munich world cup and the change in rhythm prompted by a new partner causing similar problems for Brennan. 

With reserve Jared Bidwell on standby to step in, the reigning champions came fourth in their heat and won their repechage before a fifth-placed finish in the semi-final ended all hope of another medal.

They eventually came second to Norway in the B-final for an overall eighth place and watched on as New Zealand's back-to-back world champions Nathan Cohen and Joseph Sullivan won gold.

``That was not a very nice race to watch,'' Brennan said. ``An experience like that can be so intense it's paralysing and it was seeing that race and knowing where we could have been. That's what causes the pain.

``If they are out of your league you can accept it, but everyone there we had beaten, so to watch that race was overwhelmingly disappointing.''

Since returning to Australia, Brennan has spent a lot of time mountainbiking to clear his head and after talking to friends, family and coaches has committed to carrying on to Rio de Janeiro.

He is not sure whether Crawshay will make the same decision but admitted it would feel strange rowing without his international crewmate of eight years.

``We were in really good form prior to getting all the injuries and I reckon I would have called it a day after London. But after how disappointing it was, and how hard it was, I resolved that I could not leave on that note, and I do want to push on to Rio.

``There were a lot of positives to take out of the last 12 months; leading up to the injuries we were right at the top of the field.''

Brennan is yet to determine how prolonging his rowing career will affect where he lives or works but expects to stay in Canberra, make regular trips to Hobart to see his family and continue his medical career.