There will be at least nine ultras in Hong Kong in the next year - including three new events - but none as challenging or historic as the WS100.

Semick, 46, in her fourth attempt at the race, was among the favourites after she came a close second last year to Ellie Greenwood of Scotland. USA Track and Field's Ultrarunner of the Year in 2008 and 2009, Semick moved to Hong Kong in August last year from Oregon, after her husband was transferred to the city.

Compared with Semick, Price, 43, a property agent, and Lee, 42, a civil servant, are less accomplished, nonetheless they are consistent top finishers in local races. Both started running only 10 years ago, and this was their WS100 debut.

All three are driven by a passion for long-distance running - often mistaken for a mild form of insanity. Also providing motivation is the WS100's quirky finishing medal: a belt buckle, in silver for a sub 24-hour finish and bronze for sub-30.

But just earning the right to be at the WS100's 5am start in Squaw Valley, California, deserves an award. You cannot simply sign up for the race. First you have to prove yourself at a qualifying event - run 50 miles (80 kilometres) in under 11 hours, 100 kilometres in under 15 hours, or 100 miles within the particular event's official cut-off time.

That puts you into a lottery, where you then need a tonne of luck to win one of the 369 race slots.

It's so hard to get in that even being admitted to hospital with sudden unexplained hearing loss a week before the race would not stop Lee. "This was my second attempt at getting into the race, and I was so lucky to be selected," she says. "It was an opportunity I couldn't afford to miss."

The WS100 began as a horseback challenge and, as the race guide warns, "presents numerous medical risks, many of which can be extremely serious or fatal".

So it may seem odd that anyone in their right mind would be keen to do it. What has possessed Semick, Price and Lee? All three say it's the freedom that running in the mountains gives and the deep sense of the appreciation for the world it invokes.

"I always discover small things that we overlook or take for granted," says Lee. "I think I am more grateful for life since I started running."

Price says: "It's inspiring in so many ways. There's the beauty of the natural landscapes, the camaraderie, the feeling of freedom and the exhilaration to push yourself to run further and faster."

The College of Western Idaho published a study last year in the which surveyed 344 female ultramarathon runners. It found that these women were task-oriented, internally motivated, health- and financially conscious individuals. They trained an average of about 12.5 hours a week and spent 64 per cent of their time training alone.

A 2009 study on the WS100, published in the journal found that since the race's inception, in 1974, participation had increased among women. Finish times have been improving for the top women, unlike those for the men.

Christopher McDougall, in his bestselling book , notes that the female world record for the mile (four minutes, 12 seconds), was achieved a century ago by men and rather routinely now by high school boys.

Yet at the Leadville Trail 100 mile-long race in the Colorado Rockies, nearly all the women finish the race and fewer than half the men do. "Every year, more than 90 per cent of the female runners come home with a buckle, while 50 per cent of the men come up with an excuse," writes McDougall.

Dr Duncan MacFarlane, sports physiologist at University of Hong Kong's Institute of Human Performance, links it to a female's ability to metabolise a higher percentage of fat than males. Fat is the body's main fuel source for ultramarathons.

Women are also usually smaller and lighter, says MacFarlane, so long distances take less of a toll on their bodies. They're also better at preserving themselves for the long haul. A 1997 study by University of Cape Town sports scientists in South Africa found that women ultramarathon runners have greater fatigue resistance than do equally trained men whose performances are superior up to the marathon distance.

This ability to resist exhaustion is believed to be due to not only physical factors, but also mental strength. "Put it this way, I think there'd be far fewer children if men had to give birth," says sports psychotherapist Dr Bruce Gottlieb in a article.

Price loves a challenge as much as a good chat. To her, running is a social activity, a way to make new friendships and cement existing ones. "It's about the people who share the journey with me," she says.

For Semick, ultramarathons are a sprint compared with her past life as a mountaineer: she can race and be back in time for dinner that night or breakfast the next day with her husband and daughter. "It's easier on the family than mountaineering," she says.

"And there are as many or more peaks and valleys during one day than there are in three weeks of big mountain climbing."

By the 47-kilometre mark of the WS100, the runners had battled two long climbs totalling almost 2,000 metres in ascent and a steep run down into a valley.

For the past six hours, they had endured sleet and hypothermic conditions in high winds. The high spirits that marked the race start gave way to a more sombre mood.

Yet Price was still smiling, joking that she felt "gypped" by the weather after coming from Hong Kong's hot summer. She knew the race almost didn't happen for her: a month earlier, she had fallen during a run and badly bruised her knee, forcing her to stop training.

Semick's day wasn't as good, as she dropped out around this point following a severe asthma attack. It was truly unfortunate, especially since she had been running strongly among the race leaders, men included.

In 2010, Semick finished third overall in the Vermont 100 Mile Endurance Run, beating all but two men. In the world of ultrarunning, women outperforming men isn't surprising. As race distances get longer, the gap between men and women gets smaller.

A few hours behind Price, Lee trudged on determinedly despite her ear troubles and ill preparation. "I just kept thinking: 'Keep it up; you can make it,'" says Lee. "Just one more step and you will be closer to the finish line."

It's this unbreakable spirit that got Lee to the finish at last year's Ultra Trail Mont Blanc in Chamonix, France. After 94 kilometres and with the 2,490-metre-high Grand Col Ferret ahead of her, she pulled out from exhaustion. But she became impatient waiting to be picked up by race officials, so she decided to rejoin the race. She finished the 166 kilometre race in 44 hours, 22 minutes and 38 seconds.

The same mental tenacity got Lee through the last 50 kilometres of the WS100. She finished in 28 hours, 29 minutes and 55 seconds despite crippling knee problems and stiffness. "I am not a talented or gifted athlete," she says. "I am just a normal person."

Price blazed the final 34 kilometres, picking off fellow competitors who had lost steam. She eventually finished in 18th place among women and 87th overall in 22 hours, 32 minutes and 52 seconds. To outsiders, it's an extraordinary feat. To Price, it's just another day. "You can train yourself to overcome many things you thought were impossible. You just have to put your mind to it."