A man held in Iran for nearly five years on spying charges, before being released alongside Nazanin Zaghari-Ratcliffe, says he is determined to finish the London Marathon.
Anoosheh Ashoori, from Lewisham, south-east London, was released in March.
Talking to the BBC's Today programme, the 68-year-old said he was dedicating his run to the people of Iran and its prisoners.
"I am determined to cross the finish line, if my knees don't fail," he said.
He is running for Amnesty International and Hostage International at the race on Sunday.
The British-Iranian dual national was arrested in August 2017 while visiting his elderly mother in Tehran and was later convicted of allegedly spying for Israel's intelligence service Mossad, despite having lived in the UK for 20 years. He denied all charges.
Mr Ashoori said while being held in Evin prison he started running in circles in a small prison yard, and gradually built up his stamina so he was able to run for up to two hours.
"In the prison we had very little opportunity for exercise," he said.
"We had a small yard we could run in circles which put strain on our knees.
"At one point we were banned from using all the sports facilities, the very little that they had, so we were practicing in a patio but we were determined to carry on."
Mr Ashoori said physical exercise was a "good remedy" to "fight insanity when you are going through such intense suffering".
Mr Ashoori, who will be running with his son Aryan, also urged the British Government to do more to help negotiate the release of other detainees held in Iran, like Morad Tahbaz.
He added he was running to "let all the ones who are left behind know they are not forgotten".
"What will be going through my mind when I'm running is my solidarity with the people of Iran and with the women's movement," he said.
"My heart will be with them and I hope that it will come into fruition."
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