Frank Gore this week signed a three-year contract extension that’s worth a maximum of $21 million — this in a climate where netting a new deal of any sort for a 29-year-old running back is difficult at best. But the details of Gore’s pact with the 49ers point out just how stark the market forces are for NFL running backs as years and injuries mount.

The 49ers officially activated Frank Gore from the did-not-report list Monday, according to a league source, signaling the end of the running back’s holdout.

Frank Gore has a hip injury and is questionable to return for the 49ers in Monday night’s game against the Cardinals.