Nicole Richie sunglasses work out gym spandex sneakers

Nicole Richie wore her usual all black outfit to workout in Studio City, but she left looking a little different than normal ... she seemed super tired!

The fashion designer, wearing an oversized top and leggings, clutched onto a fave jean jacket as she head back to her car Monday. The smart mama looked both ways before crossing the street, but we just can't figure out why she was hiding behind that jacket!