Some familiar faces along the offensive line once again. With left guard Charlie Johnson re-signing in the offseason, all five starters will return this season. The unit has played together the past two seasons and missed three games between Johnson, tackles Matt Kalil and Phil Loadholt, guard Brandon Fusco and center John Sullivan in that stretch

We finished last week previewing the running backs, and we continue our series with a look at the offensive line.

WHERE THINGS STAND: The returning offensive line starters combine for 28 years of experience. It's a veteran group led by Sullivan, who ranked as the third best center in the league last season according to Pro Football Focus. The unit had a slight dip in pass protection but still remained the top 10 in pass blocking efficiency, which takes into account sacks, hits and hurries allowed. The offensive line ranked ninth in PBE at 79.1, where in 2012 it ranked seventh at 82.1. The productivity dropped the most in the run protection, which in some ways was expected following running back Adrian Peterson's MVP season with 2,097 rushing yards. The offensive line carries a blend of youth, rookie guard David Yankey, second-year guard Jeff Baca and rookie tackle Antonio Richardson, and experience, center Joe Berger and guard Vladimir Ducasse, as backups. It's a good unit and that should reflect in its play barring any major injuries.

CAMP BATTLE TO WATCH: Although every starter is returning, keep an eye on rookie guard David Yankey, who'll compete with Johnson at left guard. Yankey missed most of OTAs due to school, but he already possesses great size listed at 6-6 and 315 pounds. He played in an aggressive offense at Stanford that will benefit Yankey as he makes the leap into the NFL despite missing a considerable amount of time. Johnson has been very durable in three seasons but the Vikings could use an upgrade at the position. We'd need to see Yankey more before making any claims of starting at some point this season, but it is a possibility.

THE BURNING QUESTION: Will Kalil return to form this season? He's expected to be a full participant this week in training camp after recovering from minor left knee surgery. Whether that's the reason for his subpar performance last season is unknown, but Kalil regressed from an impressive rookie season at left tackle. Defensive ends blew right by him with ease at times last year. Kalil's quarterback hits allowed jumping from four to 12 and quarterback hurries from 20 to 33 last year. Kalil still has the ability to return back to the performance level of his rookie season, that's not in question. Will he, on the other hand, is something he'll have to answer in September.