The Niners don't seem too worried about laying the extra responsibility on Hearst, who had franchise-record totals of 310 carries for 1,570 yards in 1998 before a career-threatening ankle injury forced him to miss the next two seasons.
Hearst returned last year to establish himself again as a Pro Bowl tailback with a miraculous comeback. He gained 1,206 yards, but that came on 252 carries as Barlow - in his rookie season - spelled Hearst during several offensive sequences each game and finished with 512 yards rushing. Hearst averaged 16 carries a game last year, and he remained relatively healthy throughout his comeback season.
This year, Hearst is averaging 12 carries a game while Barlow was getting an almost equal opportunity to lug the football before he was injured. Hearst is 13th in the NFC with 657 yards on 133 carries while Barlow is 16th in the conference with 514 yards on 116 carries.
Hearst was on a pace to fall just short of a 1,000-yard season for the first time since joining the Niners in 1997, but with Barlow sharing carries San Francisco's running game was as strong as ever, ranking fifth in the NFL in yards gained and fourth in average per carry.
Now Hearst appears destined to give the Niners a 1,000-yard rusher for a team-record sixth consecutive season, but the team still plans to be judicious with the way it uses him.
With Barlow not around for insurance for at least two games - and probably three - other San Francisco running backs can expect to see more carries come their way. The Niners also are a little banged up at fullback, where starter Fred Beasley is nursing ankle, knee and groin injuries.
"We'll have Garrison carry the load - he's very capable of doing that and has before," Niners coach Steve Mariucci said. "We'll probably activate Jamal Robertson as an emergency back, but you saw Paul Smith step in and do a pretty good job. He can be the backup fullback, or the backup tailback if need be. So, Beasley, Smith and Garrison will carry the load and Jamal will be the emergency guy."
Hearst, who earlier this season indicated it wasn't easy to get in a rhythm with only 10 to 12 carries a game, is the kind of back who usually gets stronger as a game progresses. And that leads quarterback Jeff Garcia to believe it might actually be a boon to the running game if Hearst once again becomes the primary featured back.
"Kevan's a great player for this team, and it's unfortunate he's going to miss (some playing time)," Garcia said. "But it might be a positive situation for Garrison. I think what it allows is for Garrison to be more of an every-down back, more of a back that might be able to find his own rhythm. It's just something where we'll have one back focusing on the task at hand instead of two backs looking to exchange time every other series."