Carrie Underwood just dropped jaws, proving her rock-hard legs might take over her powerhouse voice. The 37-year-old country superstar and 2005 "American Idol" winner has been busy promoting everything from her "My Gift" Christmas album to her 2015-founded clothing line, with yesterday bringing the latter in a fresh Instagram update. Carrie, who founded her CALIA by Carrie athleisurewear line in 2015, doesn't always appear in the brand's promos. When she does, fans go wild. Check out the killer workout look below.