It is often recommended to build up your running to 50 miles a week for various military special ops programs within the Army , Navy , Air Force and Marine Corps . While those programs involve significant running (and rucking) -- and you need to be good at both -- 50 miles a week is not a one-size-fits-all recommendation. Here is a question regarding building up to 50 miles a week and how to sustain or maintain it for more extended training periods: Stew, once you reach 50 miles a week running,