INDIANAPOLIS -- The Indianapolis Colts will be back together at the team's facility on the west side of the city for the first time since cleaning their lockers out the day after the AFC Championship, as they start voluntary offseason workouts on Monday.

The key word is "voluntary," but it wouldn't be surprising if many of the new players the Colts signed during free agency take part in the workouts so they can acclimated to their new teammates and surroundings. This part of the offseason workouts will consist of strength and conditioning.

Here are the three questions surrounding the Colts heading into their workouts:

Will the injured players take part in the workouts?

The Colts had 15 players end last season on injured reserve, and another player they signed during free agency -- linebacker Nate Irvin -- was also on IR. Offensive linemen Matt Hall, Hugh Thornton, Donald Thomas, Ulrick John and Gosder Cherilus, running back Vick Ballard, linebackers Daniel Adongo, Robert Mathis and Cam Johnson, and defensive lineman Jeris Pendleton are players still on the roster who are coming off season-ending injuries. Mathis is the player everybody is curious about. He suffered a setback with his Achilles rehab back in December and I don't expect him to take part in any of the offseason workouts, especially with owner Jim Irsay saying last month that it could be as late as November before the linebacker is ready to go. The Colts will take the cautious approach with Mathis. Keep in mind Mathis had his Achilles surgery in September 2014.

Who has the most to prove?

I think there are two players who have to step up. Linebacker Bjoern Werner went from starting in place of the injured Mathis to being a healthy inactive for the AFC Championship Game. The Colts gave mixed messages on why Werner was inactive. But no matter how you look at it, the clock is ticking on the third-year linebacker. With newcomer Trent Cole the leading candidate to start at rush linebacker (if Mathis is still out), and the emergence of Jonathan Newsome, who led the team with 6.5 sacks last season -- plus Mathis' return at some point -- Werner will likely be switched over to the strong side behind Erik Walden, where his primary responsibility will be to stop the run.

Colts coach Chuck Pagano said he plans to have an open competition for the starting center position between Khaled Holmes and Jonotthan Harrison. Holmes started the last five games of the season, but it obviously wasn't enough to convince Pagano he's definitely the answer at the position. Holmes, the team's fourth-round pick in 2013, went into training camp as the starter last season, only to go down with an ankle injury. He didn't win the starting job back until Week 16. Harrison, an undrafted free-agent rookie last season, took over for A.Q. Shipley at center in Week 5, but he wasn't overly impressive, especially when it came to delivering clean snaps to quarterback Andrew Luck.

What are the other intriguing position battles?

Chapman will be pushed by Kerr and Hughes (and possibly the team's draft picks) for the starting spot on the defensive line alongside Jones and Langford. Chapman started 15 of 16 games last season, but he hasn't dominated at the position. The Colts need a player who can take up space on the line and get pressure up the middle, especially when it comes to stopping the run.

Veteran Todd Herremans is the likely starter at guard, but you can expect Thornton, who has started there when healthy the past two seasons, and newcomer Ben Heenan to push him for the job.

This is a big if at this point, but keep an eye on rush linebacker between Cole and Mathis if the latter does end up being ready for Week 1. You also can't forget about the rising Newsome, who made a relatively smooth transition from defensive end in college to linebacker last season.