71-year-old grandmother completes 100-mile ultramarathon - with just six seconds to go

She became the first woman over the age of 70 to ever finish the 45-year-old event

Gunhild Swanson at the finish line with her legion of fans (Western States Endurance Run vis Facebook)

A 71-year-old grandmother finished a gruelling 100-mile ultramarathon in California – with just six seconds to spare before the cut-off time.

Gunhild Swanson was the last person to cross the finish line at The Western States 100-Mile Endurance Run, but she still managed to steal the show by becoming the first woman over the age of 70 to ever finish the 45-year-old racing event.

Mrs Swanson was almost certain she would never make the 30-hour cut-off point after she went off-course in the middle of the race.

Still, she managed to cross the finish line just in the nick of time at 29 hours, 59 seconds and 54 milliseconds.

Speaking with the ultramarathon website, iRunFar.com, the runner explained how, at the 88-mile mark, things started to go pear-shaped when she made a “rookie mistake.”

The race sees runners climb more than 18,000 feet and descend nearly 23,000 feet before they reach the finish line.

In between the 100 miles, participants run and climb through valleys, country and canyons and cross the ice-cold waters of the Middle Fork of the American River.

Mrs Swanson described how she followed some runners who had accidentally taken a wrong turn which is what held her back but, thankfully, her friend, Dave, was on-hand to give her the confidence she needed to keep on as he directed her along the route.

Coming into the view of her friends and family at the finishing line, Mrs Swanson realised she only had seconds to go until she reached the finish line.

With the crowd going wild when she crossed that line, Mrs Swanson said her excitement levels piqued upon hearing the roars for her, adding that the noise it was “overwhelming.”

This hasn’t been Mrs Swanson’s first sporting feat: the mother-of-four, who moved to Washington, D.C. from Germany in 1963, has been competing in ultramarathons since 1987.

She has run more than 260 races, 15 of which took place last year alone.

Despite having clinched victory at the race, the grandmother insists she won’t be doing anything spectacular to celebrate: “No matter the distance, no matter what race it is, I love adventures.

“I finished this sucker.”

Watch the moment of 'victory':