Here we go again on the search for backup help to Steven Jackson in the Rams' backfield. The free-agent additions of Cadillac Williams and Jerious Norwood looked good on paper last summer at the start of training camp.

But Williams was so-so, with some notable problems on swing passes early in the season. Norwood barely played. Both are free agents this offseason and aren't expected back.

As usual there were plenty of potential running back options on display this week at the Senior Bowl, with the headliners being Chris Polk of Washington and Doug Martin of Boise State. Both project as second- or third-round draft picks.

There are few backs in the country, or in the history of the Pacific 12 Conference, as productive as Polk with the Huskies. He posted back-to-back seasons of 1,400-plus yards rushing, and with 4,049 career rushing yards is only the seventh rusher in Pac-12 history to top 4,000.

At 5-10½ and 224 pounds, Polk is a strong physical inside runner. He's not going to make you miss, but he will run through arm tackles and rarely gets caught in the backfield for a loss.

"He's so strong in the lower body," said one veteran AFC scout. "He gets a lot of yardage after contact. He breaks tackles with his legs because he's strong."

Polk is an erect runner, meaning he takes a lot of hits. And some scouts question his speed, to which Polk takes offense.

"I've been fast my whole life," Polk said. "It's just a matter of showing it. I think they think I'm slow because of my running style. I'm real patient. If I see a crease, I'm gonna hit it 100 mile per hour."

There are faster backs in today's Senior Bowl game than Polk, but it's doubtful any have better hands. Although he never caught more than 31 passes in any one season at Washington, he did have four touchdown receptions in 2011.

When it was suggested that St. Louis wouldn't be a bad spot, complementing Jackson, Polk replied: "No, it wouldn't. I'm actually going to work with him, too. I'm looking forward to making that happen."

Jackson and Polk are represented by the same agent, so Polk will be working out with Jackson in Las Vegas later this offseason, following Jackson's South American vacation.

Martin, meanwhile, plays bigger than his size (5-9, 219), and he's not afraid to tell you so.

"I look at myself on film and I feel like I play 6-3," he said. "I play as a big back. I'm a powerful guy, and yes, I take pride in that, also."

He certainly runs that way. Although he has a quick sidestep or jump-cut, one of the things scouts like best about Martin is that he hits the hole hard. No dancing around here.

"He'll lower his shoulder," the scout said. "He's not quite as strong in the lower body as Polk, but he's another guy that can get yardage after contact. He protects the ball a little bit better (than Polk)."

Martin also has good hands as a receiver, but not as good as Polk. And both backs will pick up blitzes; Martin was particularly impressive in pass protection drills earlier in the week in Mobile, Ala.

Martin rushed for more than 1,200 yards in each of his last two seasons at Boise and scored 43 rushing touchdowns over his college career. Over his final two seasons, he caught 56 passes for 593 yards and four TDs.

"Coming from one of the smaller schools, I want to show that I can play with these big boys," Martin said. "That I can be put in any system and be able to play in the games."

Boise State showed it could play with the big dogs, small dogs, and medium dogs during Martin's career. He's part of a senior class there that posted a 50-3 won-loss record.

Among some of the other Senior Bowl backs, Baylor's Terrance Ganaway had a disappointing practice week. He looked like a straight-line runner without explosiveness.

Mississippi State's Vick Ballard may not be a starter at the next level but showed good hands in the passing game and a better burst than expected.

And then there's Florida mighty mite Chris Rainey, who measures in at 5-8 and weighed 178. Raw, fast, but unpredictable, he could be one of those "Swiss army knife" types in the NFL, playing a little wide receiver, a little running back and returning kicks. From Percy Harvin to Dexter McCluster, some of those guys have worked out — and some haven't — in the NFL lately.

"Running back's going to always be my favorite position," Rainey said, but he added, "Wherever they put me, I'm ready. Don't care as long as I help the team win."

Rainey plans to run at the NFL scouting combine and says he wants to post a 4.1-second time in the 40-yard dash (which would be only slightly slower than the speed of light).

"Set a record that nobody can beat," Rainey said.