12/20/2011 AT 05:55 AM EST
's Alexander Skarsgard
enjoyed a vigorous workout at Equinox in West Hollywood. The actor, in a baseball cap and gray and yellow workout gear, hit the elliptical machine and looked like he meant business, an onlooker says. The actor was listening to music and fiercely working out. Says the onlooker: "He was in the zone and completely focused on his cardio."