LONDON — Studying, exercise and meditation were what got Al-Jazeera journalist Peter Greste through the 400 days he spent incarcerated in Egypt.

49-year-old Greste was in London Thursday, for the first time since he was freed earlier this month by presidential decree in Egypt.

He and fellow journalists Mohamed Fahmy and Baher Mohammed, who were last week released on bail pending a retrial, were arrested in 2013 and charged with crimes that included spreading false news. Throughout the trial, all three men denied the charges, calling the trials a sham.

“The greatest danger in this circumstance is your own mind," Greste said, speaking at the Frontline Club. "You can get into a massive mind fuck."

Greste, who was incarcerated in three different prisons, said he ran between seven and 12 kilometres a day in a narrow corridor as well as following an intense exercise programme developed by the Canadian Air Force for its pilots.

"I'm in better condition than I have been in 20 years," he said with smile.

"If any of you want to lose a bit of weight, spend a year in an Egyptian prison." - @PeterGreste at the @frontlineclub — Andrew Jones (@andrewmjones) February 19, 2015

As well as working out physically, Greste started studying for a masters' degree in international relations.

Griffith University in Australia sent him a 13-kilogram box of course materials via the Australian embassy in Egypt, which he used to do his course work, writing essays longhand with a pencil.

He says he'll continue his studies now that he's released but instead of sending his assignments through the mail, he'll switch to the Internet.

With their watches taken off them, the focus every day for the Al-Jazeera three was just to get through the incarceration one hour at a time.

Greste said they discussed the prospect that one would be released ahead of the others, and agreed in such a situation that person would leave.

"Walking away and leaving them behind was not easy, I still feel quite anguished about it," he said, adding that he gave Mohammed a hug before parting. Fahmy was hospitalised at the time.

Greste, who was being interviewed by Al-Jazeera correspondent Sue Turton, one of nine journalists charged in absentia and sentenced to ten years by the same Egyptian court, was keen to highlight the other people, including a number of students, who have also been caught up in the trial, accused of being members of the Muslim Brotherhood.

The retrial of Mohamed Fahmy and Baher Mohamed, who remain in Egypt, is due to get underway later this month.