The Packers and 49ers lead the NFC, and both teams will have to manage their top backs carefully down the stretch.

This is the NFL’s tree that falls in the woods, and it slams hard into the ground every December. There’s never been a neat and tidy answer in the ancient debate between rest and rust for playoff-bound teams. All we have are injury reports, and past nightmare-inducing ligament tears in meaningless late-season games.

This year’s subjects are James Starks and Frank Gore, running backs for the only two teams in the NFL that have clinched a playoff spot, and the two teams that are leading the NFC. Starks is marginally ahead of backfield mate Ryan Grant in carries (127 to 95), with the Packers giving the touches to the hot hand. The problem is that the hottest hand is hobbled, and he has been for several weeks.

Starks hasn’t missed a game yet this year, but that 12 in his “games played” column is deceiving. He’s now been yanked from three consecutive games because of knee and ankle injuries, a stretch in which he had 62 rushing yards after recording 204 yards in his previous three games. He’s missed Green Bay’s Wednesday and Thursday practices this week, leaving the Packers faced with a similar scenario to the one Indianapolis wrestled with in 2009.

Does being undefeated trump winning another title?

The simple answer to that question is a resounding and definitive no. A regular-season record should never be placed ahead of another championship banner, even if only one team in history has achieved a perfect season. That doesn’t mean the Packers shouldn’t push for history, though, but the urge to make that final sprint could result in an unwise decision involving a player who’s clearly ailing.

Starks reportedly didn’t practice today either, meaning he’ll most likely be ruled out for Green Bay’s Week 14 game against Oakland. But even if he was able to practice, allowing him near the huddle Sunday would have been a poor decision for a team that will rely on the two very distinct running styles of Grant and Starks to be successful in the playoffs.

Packers offensive coordinator Joe Philbin told the Green Bay Press-Gazette that he’s mindful of both extremes in the never-ending late-season battle between rust and rest. As a coach, the instinct is to keep the machine oiled.

“It works both ways. On the one hand, he could be a little fresher when he heals completely. The negative is, you haven’t moved and developed and progressed as a player when you haven’t got out there, competed, made mistakes, learned and improved. From a freshness standpoint? Maybe. But not from a football development standpoint — I don’t think it helps.”

It’s about balance, and it always has been. Jim Harbaugh faces a similar balancing act with Gore, his primary runner who averaged an incredible 126.8 rushing yards per game between Weeks 4 and 9. Since then due to nagging injuries that average has dropped to a paltry 50 yards per game, including zero yards on six carries in Week 6 against the Giants.

Gore’s been limited by an ankle injury, and he missed practice time prior to last week’s win over St. Louis. San Fran sits only one game ahead of New Orleans in the race for a first-round bye in the NFC and a better position for home field advantage, making Gore’s presence vital.

Still, limiting his carries is a viable option with rookie backup Kendall Hunter capable of shouldering an increased workload, and two weak run defenses (St. Louis and Arizona) lined up over the 49ers’ last four games. But Harbaugh isn’t a fan of the idea, saying earlier this week that Gore’s carries won’t be limited, even though the Niners have already clinched the NFC West.

The risk is high with Gore, a fragile player who’s missed 12 games in his career, and has only played a full 16-game season once. And the reward is highly desirable, but perhaps not worth the sacrifice of a running back who anchors San Francisco’s offense.