During Jim Harbaugh's coaching tenure in San Francisco, the 49ers have transformed into a tough, physical football team. They have gained a well-deserved reputation for stopping the run.

In 2011, the Niners allowed the least total rushing yards and tied for first in yards per carry allowed in the NFL.

So far this season, San Francisco is 10th in yards allowed per game and are seventh-best in yards allowed per carry.

In the last two weeks, against the New York Giants and Seattle Seahawks, the 49ers' rush defense has struggled like it has never before under Harbaugh. The Giants and Seahawks averaged 142.5 rushing yards against the San Francisco 'D'.

In the other 23 games (including playoffs) during Harbaugh's tenure they have allowed an average of 75 yards rushing per game.

The main reason for the struggles has been an inability to stop the run up the middle according to the numbers provided by Pro Football Focus. New York and Seattle ran 26 times in that direction (between LG, C, and RG) for 161 yards, which is 6.19 yards per carry.

Pro Football Focus also has 49ers nose tackle Isaac Sopoaga as a -4.1 on the season, with most of that rating being earned in the last two contests.

Cardinals center Lyle Sendlein was asked specifically about this issue.

"I don't think it's a lack of ability or physicality in the middle," said Sendlein. "Sometimes defenses take away something and make you beat them one way and maybe that was their play for that week."

Going up against a Cardinals team featuring LaRod Stephens-Howling, a 5'7", 185-pound running back, it wouldn't be out of the question for the 49ers to employ a similar strategy.

It's also in the realm of possibility that Sendlein didn't want to give the 49ers any bulletin board material and say something insulting about San Francisco's interior defense.

The question is can the Arizona Cardinals exploit what has been a weakness for the 49ers the past two week on Monday night?