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The Kiwi pole vault sensation yesterday announced her withdrawal from the world athletics championship in Doha, as she takes a short break at home with one eye on next year's Olympics in Tokyo.
McCartney admitted her lingering hamstring issues – which started in August last year – have taken a toll on her both physically and mentally, ultimately leading to her decision not to compete at the world champs.
"It can be really tough," McCartney told Radio Sport.
"You know as an athlete it's your world being able to use your body to compete and physically be strong and so when that starts failing on you, you get all sorts of things.
"I've certainly had times where you can't help but think like 'maybe my body is not cut out for this, maybe I can't do this'. You know all sorts of things.
"And it has been really tough and challenging but of course I really do think that I'll probably look back and be really grateful because you learn so much through those periods and you learn a lot about yourself."
The 22-year-old said her "mental wellbeing" was an important factor in her decision to make the tough call not to compete.
"Mental wellbeing in this sort of situation is really important too," she said.
"And that's certainly one of the reasons why we came up with this decision. You've got to look after yourself.
"As an athlete you can be really stubborn sometimes and you just want to persevere no matter what and you push through everything. And I think that's a really normal response for a lot of athletes to do. So that's why I'm really grateful to have such a great team."
McCartney made her long-awaited comeback to athletic competition at the recent Diamond League event in Paris, but failed to get past the first mark of 4.25m. Her outdoor personal best is 4.94m.
She says she will focus on getting consistent training under her belt and target the indoor world championships in March next year, with the ultimate goal of competing once again at the Olympics.
"I started getting this neural hamstring issue in August last year. So it's been an entire year now, which means I've had an entire year of quite inconsistent – and most of the time quite severely modified – training.
"And I think what it came down to really is that had a bigger impact on me than what I thought it would. So it was a little bit of a shock when I started competing again that I didn't realise how much of an impact all of this modified training might have been having on me."
But McCartney is confident she'll be back and ready for the season leading up to Tokyo – and clear the 4.70m height she needs to qualify.
"I haven't been able to jump the qualifying height, which makes it a little bit tougher because I will have to obviously do that as soon as I start competition next year.
"But at the same time that's a height that I'm really confident at. So I just need to start competing and being myself again and it shouldn't be too hard."