Some Seattle Seahawks legends are part of a massive study of former NFL football players quietly underway at Harvard University.

“There was a lot that was attractive about the player’s study at Harvard. I think one of the things for me is that it was the whole body, whole person,” said former quarterback Matt Hasselbeck, who led the Seahawks to the Superbowl in 2006.

Hasselbeck is one of nearly 4,000 NFL players under examination by Harvard physicians, neurologists, cardiologists and other medical experts.

The research director of the Football Players Health Study at Harvard University says the seven-year study is the largest of its kind of professional football players.

Dr. Alvaro Pascual-Leone says the goal is to identify the effects of playing football “by developing ways to diagnose earlier, treat more effectively and ultimately prevent the consequences that may come from a career in professional football.”

“I think what I appreciate about this study is that it’s not (just) a concussion study,” Hasselbeck said when he met with KING 5 on Harvard’s campus in early January. “It’s a holistic study and we’re learning all kinds of stuff,” he said.

Hasselbeck and doctors at Harvard say there’s been an inordinate amount of attention given to brain injuries. That’s important, they say, but also point to other ailments that plague players.

“I know that certain injuries get a lot of headlines, but for me the surprising one would be problems sleeping (and) some of the heart stuff,” said Hasselbeck.

Former players experience a high incidence of heart troubles. In the last nine months alone, Seahawks Hall of Famer Cortez Kennedy died from heart disease at age 48, and former Hawks punter Rick Tuten died at 52 of a heart attack.

Dr. Ross Zafonte of the Spaulding Rehabilitation Hospital in Boston is examining players in person to understand why some suffer serious impacts from the game and others don’t.

“This is a really spectacular study because nothing’s been done like it before,“ said Dr. Zafonte.

Participation in the study is confidential, but at least a half-dozen former Seahawks have publicly stated they are taking part or confirmed their participation to KING 5 including Hasselbeck, Eugene Robinson (free safety, 1985-1995), Jordan Babineaux (safety, 2004-2010), Ricardo Lockette (wide receiver, 2013-2015), Isaiah Kacyvenski (linebacker, 2000-2006) and Harper LeBel (tight end, 1989).

Last year KING 5 surveyed former Seahawks on their health, with the majority of the nearly 120 players who responded saying they live with pain on a daily basis. And half said they believe that their brain was damaged playing football.

The Football Players Health Study at Harvard is being funded by the NFL Players Association – the player’s union. But researchers are quick to point out that their findings could have tremendous benefit to people from all walks of life.

“We feel the technology here that’s being developed as a result of the Football Players Health Study could go on to help a much larger audience and patient population,” said Dr. Martha Murray, who operates an orthopedic research lab out of Boston Children’s Hospital.

Dr. Murray is developing a groundbreaking treatment for Anterior Cruciate Ligament (ACL) injuries, a common knee injury in football.

She is in clinical trials with 120 patients testing a new, sponge-like implant that connects torn ends of the ACL, a ligament that is key to stabilizing the knee. Instead of replacing the ACL with a ligament harvested from another part of the body, Dr. Murray’s procedure allows the ACL to heal itself.

The new procedure stops the progression of arthritis after surgery, which means less joint pain than the current ACL surgery. Joint pain is one of the most common complaints among former NFL players.

Although Dr. Murray’s research is being funded by the football study, she says the surgery could benefit the up to 400,000 patients a year in the United States who require ACL reconstruction.

The Football Players Health Study at Harvard University launched nearly four years ago and is expected to conclude in about three years. The results will be made public and could alter the course of football as we know it.

Polling shows that more Americans are concerned about the physical toll of the sport. A Wall Street Journal/NBC News survey in January found that 53 percent of mothers would encourage their child to play a sport other than football due to concerns about concussions, up from 40 percent in 2014. And one-third of respondents to the same poll said they believe the NFL has done enough to reduce or prevent concussions.

Researchers involved in the Harvard study say their focus is on understanding the sport’s impacts on individual players, and they will not render an opinion on whether football is a game that is too dangerous to play.

That’s what players like Hasselbeck, who believes football today is safer than it’s ever been, want to hear.

“What I appreciate about what the doctors are doing here, is they are out to just find out the truth. If the truth is we need to get rid of football, then good – get rid of football. I don’t think that’s what we’ll find out, but if that’s what we find out – get rid of it. My feeling is we’re going to make the game better and safer,” Hasselbeck said.