One of the main forms of entertainment for Americans is watching professional sports — and the pastime is as popular as ever. That’s especially true of the National Football League: Earlier this month, more than 111 million Americans watched the New England Patriots mount a stunning comeback over the Atlanta Falcons in Super Bowl LI.

In baseball, Game 7 of the 2016 World Series attracted more than 40 million viewers to see the Chicago Cubs earn their first championship in over a century, defeating the Cleveland Indians. And more than 31 million NBA fans watched Game 7 of the 2016 championship series, in which the Cleveland Cavaliers beat the Golden State Warriors.

Over time, injuries take their toll, regardless of whether someone is a role player or a superstar.

But while few will ever claim that top American pro athletes are underpaid — in an extreme example, boxer Floyd Mayweather earned more than $220 million in 2015 from a single fight — no amount of money can buy you a new body. Over time, injuries take their toll, whether you’re a role player or a superstar.

Tiger Woods was the most dominant golfer in the world for over a decade, but at age 41, he’s found it hard to compete following seven operations on his back and knees. Last week, Woods said to Dubai’s Vision Magazine that he doesn’t think he “will ever feel great” again.

And of course, any conversation on the topic needs to note the growing concerns about concussions in football, given American football is the most popular sport in America.

The NFL has been accused of ignoring the danger of brain trauma from repeated concussions for years. It was the subject of a class-action lawsuit by more than 4,500 players and their families that the league eventually settled for $765 million. Last September, it announced a $100 million initiative, “Play Smart, Play Safe,” to prevent, diagnose, and treat head injuries.

In 2015, Newsday did a special report on NFL veterans who struggled after football due to injuries or lack of career direction (or both). In a survey of 763 former players, 42 percent said injuries have been the biggest challenge of their post-NFL life — but 89 percent said they still would have played football regardless.

For many top pro-athletes, the game isn’t just their source of income. It’s all they know; it’s their sole focus since many of them were children. So it’s no surprise many reject the idea of retiring even after multiple injuries and concerns about lifelong chronic pain.

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New York Giants lineman Roman Oben suffered a severe foot injury in 2006, but although he’d earned about $10 million in his career up to that point, he shrugged off his wife and mother when they implored him to retire. He told The Washington Post in 2013, “I knew then at 33, 34 years old, I was going to have trouble walking when I’m older,” he said. “I said, ‘I don’t care. I deserve to work as hard as I can to improve the quality of life for my family. It’s my risk. I’m doing what I’m supposed to do.'”

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Here’s a look at athletes who have paid the physical price for their sport — for better or worse.

Tiger Woods: Woods, 41, was the world’s top-ranked professional golfer for almost all of the 2000s, but outside of a short-lived return to form in 2012-13, he hasn’t won a major tournament this decade. In an interview for Dubai’s Vision Magazine last week, Woods said, “I don’t think I will ever feel great because [I’ve had] three back surgeries, four knee operations.”

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Peyton Manning: The retired superstar is one of the greatest quarterbacks of all time, but Manning’s career was in doubt after he missed the entire 2011 season due to neck surgery and was released by the Indianapolis Colts, whom he’d led to a Super Bowl XLI championship in 2007. Manning later led the Denver Broncos to two Super Bowl appearances, including a championship in Super Bowl 50 at age 39. Manning had numerous neck surgeries and told the New York Post a doctor said he will need to have a hip replacement at some point.

Tony Saunders: Baseball players tend to have longer careers than football players, but serious injuries can still occur, especially with pitchers. The act of throwing a baseball 100 mph or more puts massive stress on the shoulder and arm. Saunders was the first pick for the then-Tampa Bay Devil Rays in the 1997 expansion draft. He was facing the Texas Rangers in 1999 when his arm snapped during a pitch, and he never played in another major league game. After a second break, he announced his retirement at age 26: “I can’t do it again,” he said at an August 2000 news conference. “I don’t know what’s going to happen and I want my health.”

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Tom Brady: Brady appears to have cemented his status as the greatest quarterback of all time with his record-setting fifth Super Bowl championship for the New England Patriots on Feb. 5. Brady missed most of the 2008 season after tearing ligaments in his left knee, but he’s otherwise stayed largely healthy throughout his career. Although he’s started for 15 seasons and will turn 40 this year, he has no plans to quit. Brady’s refusal to leave the game could lead to many future injuries, as playing football over a certain age is a huge risk. After the Super Bowl victory, he told SiriusXM NFL Radio: “You know, I feel like I can still do it … I still plan on playing for a long time.”

Buster Posey: Posey’s injury in a home plate collision in 2011 prompted Major League Baseball to change its official rules. The San Francisco Giants catcher suffered a shattered leg when the Florida Marlins’ Scott Cousins crashed into him, ending the season of the National League Rookie of the Year and World Series champ. Posey did come back to help the Giants win the World Series again in 2012 and 2014. In 2014, the MLB instituted the “Posey rule,” which reduces home plate collisions by restricting the positioning by the runner and catcher.

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Wesley Walker: In a 2015 interview with Newsday, the former New York Jets wide receiver, then 59, said when he tries to get out of a chair, he feels “like a 90-year-old man.” Walker is in constant pain and “suffered so much nerve damage and muscle loss that he needs help to remove the cap from a bottle of water,” Newsday reported.

Chris Borland: The San Francisco 49ers linebacker shocked the NFL by announcing his retirement in 2015 at just 24 years old. He was coming off a strong season with the team and had not been recently injured, but concerns about brain health prompted him to call it quits. Borland said he’d had two diagnosed concussions, one while playing soccer in the eighth grade, the other while playing football in high school. “From what I’ve researched and what I’ve experienced, I don’t think it’s worth the risk,” he told ESPN.