Editor's note: This is the third installment in a five-part series on the 49ers' key competitions during training camp. Today, running back.
 
A year ago, Kyle Shanahan concocted a dramatic change to his offense that he figured would cause all kinds of problems for defenses.
 
The key component was running back Jerick McKinnon.
 
The 49ers never had the opportunity to unveil Shanahan's creation because McKinnon was lost for the season a week before the opener with a torn ACL. He is set to return this summer, but he is no longer the clear starter.
 
Former Atlanta Falcons running back Tevin Coleman comes to the 49ers. He previously played two seasons in Shanahan's system. And he opens camp with the advantage of being the only player among the 49ers' top-four backs who was healthy enough to participate in the offseason program.
 
Coleman enters a competition that includes McKinnon and Matt Breida, who led the club last season with 814 yards rushing with an impressive 5.3 yard average.
 
It is doubtful one running back will carry the load all season. But there certainly are not going to be enough carries to satisfy everyone if Coleman, McKinnon and Breida remain healthy.
 
Shanahan likely is coming up with ideas on how to best utilize the speed -- including Raheem Mostert -- in the 49ers' backfield this season.
 
McKinnon would have been the centerpiece of the offense last season.
 
The 49ers planned to show off the plan in Week 1 of the regular season. McKinnon was signed as a free agent to replace Carlos Hyde as the team's primary back. McKinnon is equally threatening to opposing defenses as a runner and receiver.
 
The combination of McKinnon, fullback Kyle Juszczyk and tight end George Kittle would force defenses to make some difficult decisions on how to cover the middle of the field, Shanahan determined. The 49ers would isolate linebackers weak in coverage and exploit that matchup.
 
If teams went small with extra defensive backs, the 49ers could overpower them in the run game.
 
Now, a lot of McKinnon's involvement in the offense will be determined by how he bounces back from his knee injury.

 

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Coleman is coming off a career-best season with 800 yards rushing with Atlanta before signing with the 49ers as a free agent. In his second season with Shanahan as Falcons offensive coordinator, he caught 31 passes for 421 yards (13.6 average) in 2016.
 
Shanahan has knack for detecting weakness in defenses. In training camp, the competition at running back will sharpen the focus on the skills Shanahan will want to highlight among Coleman, McKinnon and Breida.