Speaking to BBC Breakfast, the Queen's granddaughter said giving birth to her first child, Mia, in January, had weakened her muscles.
But she was so determined to 'get back in the saddle' that she went on a skiing holiday six weeks ago to tone up and now she's raring to ride again.
In fact, she said she is determined to win an eventing gold medal at the Rio Olympics in 2016.
Zara, 32, who is married to rugby player Mike Tindall, said: "When I first got back on it was nice to be back in the saddle but you are not very stable because your muscles are not working very well.
"Then I went skiing after six weeks, which you may think is crazy, but after that I was 50 per cent fitter than I would have been if I'd stayed home for another couple of weeks."
Asked about the impact motherhood had on her, Zara said: "I've enjoyed it...it's different. Getting your body back is the hardest."
But she said baby Mia has been a joy, adding: "I'm lucky. She's been great. She's eating and sleeping well."
Zara hasn't ridden competitively since last July, but she is poised for a return at the Symm International Horse Trials on the Hambleden estate in Henley-on-Thames on April 19 and 20.
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