Nearly 1000 competitors, most from the ACT and NSW, converged on Canberra for the race's final edition on Saturday.

Entrants raced over a 50km or 100km course starting from Kowen Forest, taking in Sparrow Hill before finishing at Stromlo Forest Park.

Numbers have steadily declined since Capital Punishment began in 2009, when nearly 2500 competitors started.

Capital Punishment is still one of the biggest mountain biking events in Australia.

McMaster blamed the decreasing numbers on additional mountain bike events which have sprung up around the country in the past few years.

"There's a lot of mountain biking races at the moment, the numbers have gone down quite a lot," McMaster said.

"All events are going down because there is so many more.

"Ultimately, it is my business, I don't have another job, this is what I do, so I've got to be able to feed my kids and pay the mortgage."

Capital Punishment is one of a number of events run by Adventure Racing Outdoor Challenges Sport.

Other events include North Face 100, Kayak for Kids, the Angry Doctor MTB and various adventure races.

"It's a bit sad, but it's been seven years and we run other events," McMaster said.

"I've got two small kids, it's a family business and you've got to make choices.

"We sort of had a thought we maybe we wouldn't do it this year, then we thought we'd go ahead anyway."

McMaster said ACT competitors made up roughly 40 per cent of the entrants for Capital Punishment, with a large contingent from NSW.

There were also competitors from South Australia, Western Australia, Queensland and Victoria.

She said the event was expensive to run, with a lot of road crossings, and very logistical.