An injury to her right ankle had undermined preparations for the 30-year-old reigning Olympic 200 and world 400m champion,  but she came through the first part of her week-long test at Hayward Field as she won the US title at the longer distance in 49.68sec, the fastest time run this year.

"Two months ago I couldn't even walk,” she said. 

“Somehow we found a way."

Felix is used to multi-tasking at major championships, having competed in four events at the London 2012 Games, leaving with golds in the 200, 4x100m relay and 4x400m relay and finishing fifth in the 100m.

But a year before that her attempt at the same double she is attempting now misfired at the International Association of Athletics Associations’ World Championships in Daegu as she had to settle for bronze in the 200m and took silver in the 400m despite clocking a then personal best of 49.59.

Now she has re-set her sights, and she has three days to rest before returning to the fray for Friday afternoon’s 200m heats.

"At the beginning of the year, it seemed like nothing was going my way," she said.

"After winning the 400 here I think I was just like, 'Thank you, Lord,'.

"It's been a tough year, and it was a relief. I have put in so much work, and to see it all come together when two months ago I was barely walking - to be at this moment is pretty unbelievable."

Just as they did for Michael Johnson at the 1996 Atlanta Olympics, the IAAF and the International Olympic Committee have altered the schedule to help facilitate Felix’s double quest.

If the plan works out in Rio, Felix will run a 400m semi-final on the evening of August 14, and will then have around 13 hours before the heats of the 200, and then another 13 hours before the 400m final.

The original schedule had the 200 heats and 400m final in the same evening session.

 “It’s awesome to know that if I am able to make it, it’s going to be a little better schedule,” Felix told Associated Press earlier this year. 

“It’s motivating to know that it is real. I just have to do my part.”

Felix is not the only sprinter who needs to do their part in keeping the ambition of an individual Olympic double alive – Justin Gatlin made it clear that he is still a formidable force at the age of 34 as he won the first part of his 100 and 200m double at the trials in 9.80sec, the fastest achieved this year.

The 2015 world 100m silver medallist has less time to recover as he is back in action in the 200m heats on Thursday (July 7) evening.