Karen Arvizu

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Spc. Karen Arvizu, left, puts on her hydration pack in preparation for her role as a volunteer in a physical demands study, Tuesday, Feb. 25, 2014, in Ft. Stewart, Ga. The Army is conducting a study that will determine how all soldiers, including women, for the first time, will be deemed fit to join its fighting units from infantry platoons to tank crews. (AP Photo/Stephen B. Morton)