For thousands of years, professional armies have set physical fitness standards that rely on marching with a heavy load, and running fast without one. The original Greek Olympics grew out of the competitions that developed when soldiers sought to see who was the most fit for combat. In the U.S. Army, elite infantry armies set a minimum standard for marching with an 80 pound pack. The minimum standard is 12 miles in three hours. This is about what Roman soldiers were expected to do over 2,000 years ago. Running standards are vary, depending on the type of soldier and age. For the youngest troops (17-21), the army wide standard is two miles in at least 15 minutes, 54 seconds. For elite infantry, it's five miles in less than 40 minutes (in some units, it's four miles in 32 minutes). Other tests used are sit-ups, pushups and pull-ups. Standards vary for gender, as well as age. Except in the Special Forces, where everyone considered fit for field duty must meet the 17-21 year old standards no matter what their age. That's why you usually spot a special forces guy in civilian clothes. He's usually in his thirties, very serious and alert, and very buff.