While the career projections for frequently used running backs are quite clear -- they still have one of the shorter lifespans in the NFL and that number significantly decreases with heavy usage -- NFL coaches and general managers are starting to sound uniform in their opinion that it doesn't really matter. The Steelers aren't going to temper Le'Veon Bell's workload in his prime to squeeze out a few more years in Bell's thirties. The Dallas Cowboys will almost certainly approach the 300-carry mark with Ezekiel Elliott in 2017. This window of time is almost always the best and most valuable a running back is ever going to be.