For the first time in 16 years, the F.B.I. is requiring that its agents pass a fitness test.

"The lives of your colleagues and those you protect may well depend upon your ability to run, fight and shoot, no matter what job you hold," James B. Comey, the F.B.I. director, said in October in an internal memo to agents that was obtained by The New York Times.

The fitness tests, which started at the end of last year, are a return to a tradition begun by the F.B.I.'s first director, J. Edgar Hoover, who obsessed about his agents' weight, as well his own considerable girth. More significantly, the tests are a response to concerns throughout the bureau about how its transformation after the Sept. 11, 2001 attacks has put more stress on the agents and given them less time for fitness.

The F.B.I.'s 13,500 agents worldwide have until October to take it and the results will be included on their annual performance reviews. The test is primarily designed to ensure that agents can move quickly during a mass shooting, chase suspects and restrain them if they resist arrest. There are no weight limits, but agents have to achieve certain requirements in four different exercises depending on their age and gender.