Stanning (left) and Glover are unbeaten in 39 races

Two-time Olympic champion Heather Stanning has announced her retirement from rowing, ending her all-conquering partnership with Helen Glover.

Stanning, 31, and Glover became GB's first female rowers to win back-to-back Olympic golds when they retained the coxless pairs title in Rio this year.

Their Olympic gold at London 2012 was the hosts' first of the Games, and also the first in British women's rowing.

"I don't feel I've got anything else to prove to myself," said Stanning.

The double world champion ends her rowing career having not lost a single race alongside Glover since the World Championships in Slovenia in 2011, their dominance in the women's pair since extending to 39 consecutive victories.

Rowing retirement decision difficult - Stanning

Stanning, promoted to a major in the British army at the beginning of the year, told BBC Sport she knew "quite quickly" after winning in Rio that she would not be competing in Tokyo 2020.

"I wanted things to get back to normal before I made the decision firmly and I wanted to make sure it was the right decision," she added.

"It's about time I made the decision and it has helped me focus on what to do next, certainly with work and the army because I know that's something I want to go back to.

"It seemed the right time to make that decision."

Stanning, who followed her London 2012 gold with a tour of Helmand Province in Afghanistan, said she doubted whether she had the desire to maintain the sporting standards she had set herself.

"If I was honest with myself and said I was going to commit to another four years, would I have the same drive and determination I had four years ago?" she said. "Probably not - therefore is it worth half-heartedly committing to something?

"There was no pressure on me to make a decision this year. I could have taken a whole year to make that choice, but I wanted to know what I was doing.

"As last season progressed I realised I'd achieved all I ever thought I could in the sport and, as you get older, it gets harder. I'm quite content with what I've achieved."

Glover (left) and Stanning celebrate winning gold in Rio

Stanning added that she did not want to start resenting having to make sacrifices for her sport and wanted to "100%" focus on life in the army.

"When you commit so much of your time to one thing you end up sacrificing an awful lot of other things and it's worth it for a time, but there comes a point where you wonder whether it is still worth making those sacrifices," she explained.

Stanning said neither Glover, 30, her coach Robin Williams, nor close family and friends were surprised by her decision.

Her conversation with close friend Glover was not emotional or awkward, she said - adding that her retirement did not signal the end of Glover's rowing career.

Secrets of Glover & Stanning's success

"It does have an impact on her, but it doesn't necessarily change her mind with what she wants to do," said Stanning of Glover, who married naturalist and television presenter Steve Backshall in September.

"It seemed a normal, natural conversation, and I'm sure it was of no surprise to her. She knows me so well.

"It will be the end of our partnership in a rowing boat but it's not the end of our friendship and that's just as important."

Glover has experienced success with a different partner in the past.

In 2013 she forged a winning partnership with Polly Swann. The pair became world champions that year, while Stanning was in Afghanistan, and European champions in 2014 after Stanning took an enforced break because of fitness concerns.

"It was a great success and hopefully people enjoyed watching and supporting us as much as we enjoyed being part of it," said Stanning of her partnership with Glover.

"We both worked hard. Hopefully people will look back and see two individuals who had their opportunities and absolutely made the most of their time while they were able to."