Imagine swimming 3.86km in open water with competitors who try to hit you and pull you underwater. Then, cycling 180.25km - more than three times the length of Singapore - before running a full 42.195km marathon.
This is the Ironman race - considered to be the most gruelling race on earth. Few athletes would even contemplate taking on the quest, let alone going professional.
Yet, being a professional Ironman is precisely what Choo Ling Er wants to become. With a personal best of 4hr 46min in the half-Ironman race, she believes the goal is within her reach.
The 29-year-old said: "Most (female) Ironman world champions are 34 or 35 so I'm still at a very good age to improve. If I can hit 4:30 I'll definitely turn pro. I need to work harder but it's possible... I just need to be positive."
The Straits Times spoke to the easy-going Choo on Tuesday at Specialized Singapore - a bicycle store - where she was having her racing wheels swopped for training ones after touching down in Singapore only a few hours earlier.
She had just returned from the Ironman 70.3 World Championship in Australia over the weekend, where she came in 22nd in her age group (25-29). She clocked 5:03:27 - 33:02 (swim), 2:45:08 (bike) and 1:37:18 (run), setting a personal best for the running split.
The 70.3 mile (113km) race - also known as a "half-Ironman" - comprises a 1.9km swim, 90km bicycle ride and a 21.2km run.
But that is only half the distance she will cover when she travels to Hawaii to compete in her third Ironman World Championship next month.
Choo completed her first half-Ironman when she was 20, after graduating from Singapore Polytechnic. She did cross-country in school, but picked up swimming only in her second year in poly after an injury stopped her from running for a few months. She soon found herself in an inter-school biathlon and picked up cycling soon after to complete the trio.
Nine years on, and she is coached by German triathlon coach Jurgen Zack, who has eight Ironman titles to his name and was runner-up in the World Championship in 1997.
Zack, who trains professional Ironman athletes in Phuket, helped Choo cut her 11:00:53 time from last year's World Championship to 10:18:12 - believed to be a national record - in New Zealand in May.
Choo made headlines in 2011 when she completed a full Ironman race after recovering from a car accident in 2009 that had left her with two broken legs and out of the sport for a year.
She now has titanium plates in her leg and scars to remind her of the accident. "Titanium so they last a lifetime," she says. However, the accident left her with much more.
"A lot of times in the morning before I opened my eyes I would hope the whole thing was just a dream and I wouldn't see my wheelchair or crutches by my bedside," recalled Choo.
"Now every time I wake up and don't feel like training, I remind myself of that one year I couldn't do all this.
"Now, I just treasure it. "
