Jessica Ennis - going for gold

In Istanbul this weekend she undergoes one of the most important phases of her preparation when she defends her pentathlon title at the world indoor championships. Multi-event competitors tackle five events at indoor championships, as opposed to seven outdoors. But there will be no less significance to the showdown with her chief rival.

At the outdoor world championships at Daegu, South Korea, Ennis was narrowly beaten by the Russian Tatiana Chernova. It was one of the shocks of 2011, but Ennis has taken the hurt and transformed it into fuel for her winter training.

They meet again in Istanbul, with Ennis in breathtaking form so far this season. On one astonishing afternoon in Birmingham last month, she recorded her best-ever long jump and won the 60m hurdles with the fastest time in the world this year. Overall, there is a buzz about her performances that is fired by the desire for revenge.

An important psychological blow can be landed in Turkey. And such is her form that Ennis could go close to breaking the pentathlon world record that has stood for 20 years.

But her target is the Olympics. She missed the 2008 games in Beijing because of a badly injured right foot. The dread of colliding with such ill-fortune keeps athletes awake, for if they aren’t close to being crocked, they are simply not working hard enough.

The setback forced Ennis to make changes. For the long jump, she switched her take-off leg from right to left, easing the pressure on the foot. It was like “learning to write with your wrong hand,” she said.

The gamble paid dividends when she was crowned world champion in Berlin in 2009. She had emulated great Britons like Daley Thompson, Denise Lewis and Mary Peters in claiming the title of the world’s finest all-round athlete.

Four months later, at the BBC’s Sports Personality of the Year celebration, she was voted into third place behind Ryan Giggs and Jenson Button. Crossover status had arrived at the doorstep of the girl who appeared to have it all.

Mike Costello is 5 Live's athletics correspondent

This is an edited version of an article from the issue of Radio Times magazine that went on sale 6 March 2012.