Vikings coach Mike Zimmer was curious and concerned after three of his starters injured their pectorals, including two season-ending tears, in a seven-month span. And when a fourth player, cornerback Josh Robinson, was sidelined by a pec injury in June, Zimmer had seen enough.

"That was kind of the straw that broke the camel's back right there," he said. "That was kind of a freak one too — he fell on it. Sometimes, these injuries happen. I don't know if they're preventable but it's my job and our responsibility to look into every possible way that we cannot have those."

Eyebrows were first raised during the 2014 season, when both right guard Brandon Fusco and right tackle Phil Loadholt tore pectorals in games.

When Zimmer took the just last winter, he worked with new strength and conditioning coach Evan Marcus to overhaul the team's weight program. The Vikings had previously been using a lot of machines. This regime preferred free weights, so the weight room at Winter Park was changed.

Only defensive end Brian Robison was directly injured in the weight room. He strained his pec working out at Winter Park in May. Zimmer said that Robison was on his second set (of what was presumably the bench press) and didn't have an excessive amount of weight on the bar.

Zimmer doesn't believe that free weights are the reason for the injuries.

"I know one thing — we're stronger," he said. "The way we're doing things, we're more physical in our mentality. I changed the weight program because I want our football team to have a certain type of mentality. I want them to have a certain type of aggressiveness. I believe that's a lot about mindset as well. When you're down there and you hear those weights banging and guys working and sweating their rear ends off together, I think it's important that we do it that way. Maybe I'm just old school, but I believe that."

So the free weights aren't going away. But the Vikings are tweaking what they do with them. For example, they will try to spend more time building up the rotator cuffs because the information Zimmer gathered showed that strengthening that area will help prevent pectoral tears.

The Vikings also want to change the way they spot players when they are lifting. They added another strength coach for training camp to help with that, but Zimmer said it's on the players to support each other.

"When you're spotting a guy, it's part of your job to keep him healthy," Zimmer said. "You can't be over talking or sitting and listening to music. You're paying attention to what's going on here."

Zimmer said "a lot of people have told us that it's just freak luck," but the Vikings weren't just going to sit back and chalk the injuries up to chance.

"Always when we get more than one type of injuries, and especially pectoral that is, it's more of an unusual injury, you have to figure out," Zimmer said. "We've researched it and we're hopefully on top of it."