As you hit the gym this Halloween week, don’t leave your holiday spirit at the door. Use a little ingenuity to give your fitness ‘fit a trick-or-treat twist. We’ve got cheeky, cheerful, and downright creep-tastic ideas for Halloween fun at the gym. Here are our fifteen favorite pieces to make this Friday’s workout a bit more spooky. As if a super-set of burpees wasn’t scary enough…