There's a reason why Emmitt is the all time leader...
His records won't be broken for a while if ever, the average NFL RB comes nowhere near Emmitt in terms of durability.
Thomas Jones seemed to have played forever and even he is nowhere near Emmitt.
Using one of the best ever to set the median is a poor example..
The quote I responded to was this:
'Any RB will run out of gas after 3-4 years of getting 20+ carries a game.'
Emmitt Smith is one player who that's not true for. There are also a number of other backs it's not true for (in no particular order); Thurman Thomas, Barry Sanders, Ricky Williams, Earl Campbell, Willis McGahee, Frank Gore, Fred Taylor, Corey Dylan, Chris Johnson, Jamaal Charles, Adrian Peterson, Priest Holmes, LaDainian Tomlinson, Edgerrin James, Marshawn Lynch, Marcus Allen, Walter Payton, Stephen Jackson, Jerome Bettis, and really... the list goes on & on.
It's really not that rare for a back to carry out a heavy workload for more than 3-4 years. Emmitt was just the most Cowboys-centric example that came to mind. It was my way of disagreeing that DeMarco would necessarily be "out of gas" in 3 or 4 years as a feature back. Clearly, more than just Emmitt have accomplished the task...