U.S. Rep. Gabrielle Giffords of Arizona has started aggressive physical therapy after opening her eyes and becoming more and more alert, according to the medical team treating her.

The congresswoman was able to move both legs on command while sitting supported on the side of the bed with her legs dangling over the edge, the University Medical Center in Tucson said Thursday.

 I have to say this is a major leap forward, said Dr. Michael Lemole, the head of the University of Arizona's surgery department. This is a major milestone for her. We're hoping she crosses through many more.

Giffords first opened her eyes on Wednesday evening while surrounded by friends, according to the center. While she continues to show encouraging signs of recovery, she remains in critical condition at the center's intensive care unit.

Lemole explained that her eye opening implies that not just those parts of the brain that process commands are there, but the parts of the brain that let us awake from sleeping, our arousal center, those are starting to work spontaneously.

She's starting to become aware of her surroundings and the appropriate context of family and friends, he said.

A major concern for doctors after the shooting was brains swelling, which was expected to reach its peak at three to five days later.

On Thursday, Lemole said that was becoming less of a concern. Other potential problems remain, however. The surgeon said he continued to be vigilant about that as well as pneumonia and blood clots.

Dr. Peter Rhee, medical director of UMC's Trauma and Critical Care unit said the breathing tube would need to be removed in the next several days. He and Lemole would determine if she could breathe on her own or create a hole through the front of the neck and into the windpipe, a procedure known as a tracheotomy.

As of Friday there were three other patients related to the January 8 shooting which killed 6 and injured 14, including Giffords who suffered a shot through the head.