Killeen had been interested in cycling from a young age, but a trip to the Malvern Classic introduced him to cross-country cycling when he was about thirteen.[2][3] He had previously been interested in motocross.[4]
Career
Killeen competing in the British Cycling National Trophy, 2010
Having won multiple titles both at the junior and Under-23 levels, he competed at the 2002 Commonwealth Games in Manchester, where he took the bronze medal. Despite having won his first major medal at the international level, he continued to compete in Under-23 events, winning the silver medal at the Under-23 World Championship in 2004.[4]
Prior to the 2004 Summer Olympics, he won the test event on the Olympic track in Greece. Competing in the Games themselves for the British team, he was held up by a crash early on in the race and ended up finishing in fifth place, outside of the medal spots.[5]
He returned to the English team at the 2006 Commonwealth Games in Melbourne, Australia. Having placed third at the previous Games, he went two places better, taking the gold medal for his country.[6] In 2007, he suffered from chronic fatigue syndrome and could not compete for an entire season.[2]
He competed once more for the British team at the 2008 Summer Olympics in Beijing, and was considered one of the favourites for the gold medal.[5] Only 150 metres (490 ft) into the race,[2] his handlebars clipped a race marker, flipping him over the bars and off the bike. This left him in last place chasing the rest of the pack, but he managed to move up to seventh place by the finish.[5] He did not get the chance to defend his gold medal at the 2010 Commonwealth Games as mountain biking had been dropped from the games, replaced by archery in the schedule. He considered a switch to road racing to take part in the Games.[7]
He was selected as part of the British team to compete at the 2012 Summer Olympics in London,[8] where he hoped to achieve a podium finish,[2] but crashed out on the second lap of the race. He was the only athlete competing for Britain in the men's cross country.[8] As part of his training, he conducted practice runs at the Olympic track near Southend.[5]
He competed at the 2014 Commonwealth Games, finishing in 6th place.[9]
