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The Pentagon ordered last year that women must have the same opportunities to serve in combat jobs as men, with thousands of positions slated to open to both genders in 2016. And while an Army survey shows only a small fraction of women say they want to move into combat jobs, it also revealed soldiers from both genders are nervous about the change.

With roughly one in five Army positions considered combat-related, commanders are turning to science to find a unisex standard to judge which soldiers physically have the right stuff to fight wars.