Olympic champion Wayde van Niekerk wants to set an "untouchable" 400m world record as his legacy.

Athletics legend Michael Johnson held the record for 17 years before Van Niekerk beat it in the Rio 2016 final.

From the highs of becoming Olympic and world champion in 2017, the South African has missed most of the past three seasons with injury - but now wants to run under 43 seconds.

"I have this deep desire to be out of reach," the 28-year-old told BBC Sport.

"And after coming out of a period of somewhat suffering, it makes me more hungry."

Thursday marks a year to go to the rescheduled Tokyo Olympics in 2021.

And in a wide-ranging interview with Johnson for the Olympic Secrets series on BBC iPlayer, Van Niekerk also revealed:

His talent for the 400m event helped give him confidence to beat the school bullies;
He was in tears prior to his Rio Olympic triumph as he feared his body would break down;
Usain Bolt had predicted to him that he would break the 400m world record in Rio.

At the Rio Games, Van Niekerk ran 43.03 on his way to winning 400m Olympic gold, surpassing American Johnson's mark of 43.18, set at the World Championships in 1999.

However, in October 2017, weeks after retaining his world title in London, Van Niekerk ruptured knee ligaments in a celebrity touch rugby match in his homeland.

Van Niekerk has accepted it was "the worst decision to make" after four years of success on the track.

"I knew how to play rugby but I hadn't touched a ball for eight years," he said. "My body was conditioned for running straight - not zig-zags.

"That was the last thing I was thinking of but later on you sit back and realise that the decision was obviously silly."

He admitted to struggling with his mental health after the injury.

"The first two weeks were very difficult and showed signs of me climbing into a dark space," he said.

"So I had to bounce back because I can't be dwelling in this dark space. I had to start from scratch; I had to tell myself from the beginning that I need to take responsibility for the decision I've made."

Having had to sit out 2018 and most of 2019, Van Niekerk's 2020 has also been on hold because of the coronavirus pandemic.

Now he is keen to resume racing in order to work towards becoming the first man to break the 43-second barrier for 400m.

"It's definitely a priority for me, because why am I still here if I'm not seeking growth?" said Van Niekerk.

"Growth should be improving my times within the 42-second range. That's where my mind is at; that's where my heart is at.

"Seeing you [Johnson] set a standard of setting a record of 17 years - I want to double that.

"That's just the competitor in me and for me to settle for anything less than that would mean I'm doing an injustice to myself and the team working for me."