The most crucial factor in sporting success is probably self-belief, according to the retired Olympic rower and five-times gold medallist Sir Steve Redgrave.

"What separates the achievers," Sir Redgrave writes in his new book, "is nothing as tangible as split times or kilograms. It is the iron in the mind, not the supplements, that wins medals."

In an exclusive extract from his forthcoming book, Inspired, which recently featured in the Telegraph, Redgrave credits his success to his unshakeable sense of self-belief.

He added that his main source of inspiration is the iconic boxer Muhammad Ali, who he credits with having an insatiable desire to succeed.

"God knows, rowing hurts," Redgrave explained, noting that there is a stubbornness of mind that "acknowledges the physical pain, but discounts it for a higher purpose".

Since retiring from competitive rowing, the Olympiad has turned to other kinds of fitness training, such as taking part in the 2006 Flora London Marathon.

However, he always comes back to the Concept2 indoor rowing machine, which formed one of the main building blocks of his training throughout his career.