Gone are the days of the workhorse running back. Yes, we still have some exceptions, but in the 2019 National Football League, a back handling even 40% to 50% of their team's carries is getting high-end volume.

In fact, if we look at the 32 backs who saw the highest rush attempt market shares in the 2018 season, the median mark was only 46.3%.

So when a team is willing to give a back big volume, that's something worth looking at closely, especially in fantasy football, where volume is by far the most important factor for a running back.

Six backs that finished top-26 in market share in 2018 are set to become unrestricted free agents when the league year starts in a couple of weeks. That creates the potential for massive shifts in fantasy value.

Some teams are set to lose the bulk of their carries and have no clear heir apparent to the volume. These would be prime landing spots to boost the fantasy value of a free agent or early-round rookie back.

For other teams, they're losing a committee member that may have been holding back the value of some other players in the backfield. These are spots that could see fantasy football stars emerge out of what were middling season-long numbers in 2018.

Let's get right into it and look at which backfields have the most volume available heading into the 2019 season.