[1] She won the bronze medal for the 400 metres, and ultimately, led her national team to claim the sprint relay title at the 2009 Summer Universiade in Belgrade, Serbia.

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.

She also achieved a top-ten finish for the relay team at the 2007 Pan American Games in Rio de Janeiro, Brazil, and had won two individual silver medals at the national trials.

In 2008, Muir set her personal best, and attained a B-standard time of 51.77 seconds at the Harry Jerome International Track Classic in Burnaby, British Columbia, which earned her a qualifying spot for the Olympics.

[10] In 2016 Muir moved to UK based coach Nick Dakin where, along with winning a number European races she broke her 8 year old Personal Best, running 51.05 in Madrid.