Career
Muir made her international debut at the 2005 Pan American Junior Championships in Windsor, Ontario, where she captured the silver medal for the 400 metres, with an impressive time of 52.38 seconds. Muir became the youngest track and field athlete to represent Canada at the 2008 Summer Olympics in Beijing, where she competed for the women"s 400 metres. She ran in the second heat against six other athletes, including Italy"s Libania Grenot and Botswana"s promising track star Amantle Montsho.
She finished the race in third place by one hundredth of a second ahead of Cuba"s Indira Terrero, with her personal best time of 51.55 seconds.
Muir advanced into the next round of the competition, as she secured the final mandatory qualifying slot in the second heat. Muir, however, fell short in her bid for the final, as she placed seventh in the semifinal rounds, with her slowest possible time of 52.37 seconds.
At the 2009 Summer Universiade in Belgrade, Serbia, Muir captured the bronze medal in the women"s 400 metres, finishing behind her teammate Esther Akinsulie by thirty-seven hundredths of a second (037), with a time of 52.07 seconds. She also displayed a spectacular performance by pacing the women"s 4×400-metre relay team to a gold medal triumph.
At the 2010 in Delhi, India, Muir missed out of the medal podium, as she placed sixth in the final by more than two seconds behind her former rival Montsho in the 400 metres.
She initially finished fourth for her national team in the women"s 4 × 400 m relay. However, they were immediately upgraded into the bronze medal position, following the disqualification of the Nigerian team Muir currently resides in Edmonton, Alberta, and trains for the Legacy Athletics Club under his head coach Kevin Taylor, who is also a director of the Canadian Athletics Coaching Centre.