The Miami Dolphins will kick off their 2016 training camp on Friday.

Here are three position battles to keep an eye on this summer:

No. 1: Running back

Competitors: Jay Ajayi and Arian Foster

Analysis: This wasn’t a competition until last week. That's when the Dolphins signed seven-year veteran running back Arian Foster, who is a former Pro Bowler but played just four games last season due to an Achilles injury. Foster has the experience, but Ajayi has a four-month head start in new head coach Adam Gase’s offensive system. This should be a close race in training camp that could come down to durability. Both tailbacks have a history of injuries the past few seasons.

No. 2: Defensive tackle

Competitors: Earl Mitchell and Jordan Phillips

Analysis: This is a classic battle between an established veteran and a young upstart. Mitchell, 28, started 12 games for Miami last season. He suffered through injuries and finished with 22 tackles and zero sacks. Phillips, a 2015 second-round pick, started the other four games. He showed flashes and finished with 19 tackles and two sacks. They split starting reps in the spring, and the winner of this battle will play opposite Ndamukong Suh.

No. 3: Cornerback

Competitors: Xavien Howard and Tony Lippett

Analysis: The Dolphins will have three new starters in the secondary this year. Perhaps the biggest unknown is the No. 2 cornerback position. Howard, a rookie who was taken in the second round, showed impressive athleticism in the spring and has the inside track. Lippett is trying to stay in the race but, barring injury, probably will be a backup to provide depth.