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Ten or 20 years ago, Nate Newton and William "The Refrigerator" Perry were on a short list of larger-than-life rarities in the NFL. The 300-plus-pound behemoths made headlines simply for existing. Their every move shook the field and made people take notice.

These days, though, players their size hardly make a dent. Such is life in the ever-expanding world of the NFL.

An analysis of league rosters shows the number of 300-pounders has risen dramatically over the decades: From a single player (Gene Ferguson of the Chargers) in 1970, to three in 1980, 94 in 1990, 301 in 2000 and 394 in 2009.

"Amazing, if you think about it," said Michele Macedonio, who has worked as a nutritionist for the Cincinnati Bengals for most of the past decade, when told of that figure. "The question they have to ask is, 'How big is big enough and when do we stop getting bigger and think more about getting stronger and healthier and better?'"

Like workers in any competitive business, NFL linemen know what they have to do to keep their jobs, and in this case that means staying big. So, this August is once again littered with scenes of 300-pounders sweating through hot training camp practices. The dangers of the combination of heat, sweat and weight were brought to the fore in 2001, when 335-pound Korey Stringer died of heat stroke during camp. There haven't been any heat-related deaths in the NFL since, which in turn has dulled the debate over whether the NFL is becoming an overweight league.

But the biggest players never forget the perilous edge they're on. They live with it every day.

"It's been a struggle, but it's something you've got to work through," said Redskins nose tackle Ma'ake Kemoeatu, who was in the 400-pound range last season when he tore his Achilles while playing with the Panthers.

A struggle how?

"Eating right, getting back in shape. I have a weakness — food. My weakness is a piece of steak," Kemoeatu said.

There were 532 players in the 300-pound-plus club heading into the 2010 training camps. Certainly, it's possible some use — or have used — performance-enhancing drugs and slipped through the NFL's testing system to get to where they are. And some of this season's weights may be inflated now that a bright light has been shined on products such as StarCaps — the banned weight-loss supplement that led to the suspensions of a handful of players.

For the most part, though, the big players come by their girth honestly and are forced to walk a tightrope.

They spend the offseason in the weight room, trying to build muscle to bring their weight up. They sweat through practices, sometimes in conditions that are not conducive to anyone, let alone a 300-pounder, running around in full pads. Then they eat. They often eat between 5,000 and 8,000 calories a day, much of it in training-table meals the teams try to make low-fat and healthy. The goal is to keep the weight on in a healthy way — if there is such a thing as a healthy 350-pound man — lest they be pushed around, either by a teammate in practice or another team's player when games start for real.

Kris Jenkins of the New York Jets has been on the tightrope most of his life. He recently dropped 25 pounds, to get to 365, by going on a so-called "cookie diet," in which he eats 90-calorie bites of something that looks like a muffin top and contains milk, soy, whole-wheat flour and other ingredients.

"It was something that I realized I got to the point that I wasn't going to be able to stick around the game for too much longer if I didn't take better care of myself," Jenkins said, when asked what prompted the diet.

As the players get older, the work gets tougher. Of the dozen-or-so players interviewed by The Associated Press for this story, almost all acknowledged that they've either had to become more disciplined as the years have passed, or are seeing the day when the "eat anything you like" method will have to go away.

"I don't want to get any higher than 340," said Bengals 11-year veteran guard Bobbie Williams. "As you get older, you don't want to get the weight on you. You want to be able to move and keep up. You don't want to feel burdened down by your weight."

Yet at 340 pounds, Williams hardly stands out in today's NFL. It's a sign of how much things have changed.

Stats LLC provided the AP with a statistical snapshot of four NFL rosters — the Saints, Colts, Bears and Steelers — at the start of each decade, beginning in 1970.

The Bears — the brawny, bruising, so-called "Monsters of the Midway" back in the day — didn't register their first 300-pounder until 1990, when The Fridge (at 335) and William Fontenot (300) were on the team. (They both were on the team earlier, as well, but the study only looked at years ending in "0." The weights, in most cases, were what the players weighed in the last year of their career.)

Likewise, the Steelers won all four of their 1970s Super Bowls without a single 300-pounder on the roster. By 1990, they had four.

The Colts and Saints — last year's Super Bowl teams — combined for 10 players on this year's preseason roster at 330 pounds or heavier.

According to heights and weights listed on rosters, 97 percent of 2,168 NFL players had body-mass indexes (a formula that considers weight and height) of 25 or greater, which is considered the threshold for the "overweight" category. The BMI is often considered an unfair gauge for NFL players because they lift weights extensively and have naturally large frames. Still, it's notable that 56 percent have BMIs of more than 30, which is the threshold for obesity, and 26 percent are at 35 or greater.

It's a recipe for problems, whether in the midst of a career or after, in a sport that beats up players like no other.

"Your joints are going to be aching," said Steelers offensive lineman Max Starks, who by almost every account, carries his 345 pounds quite well. "Your joints aren't going to be able to take all that pressure because they've been taking all that abuse from playing the sport, because it is barbaric at times, it's a grueling sport and you're going to have injuries."

There's no sign of things lightening in the college ranks. Macedonio cited another study that showed a sampling of collegiate offensive lineman averaged 27.4 percent body fat — the healthy range is 8 to 19 percent — and that 69 of 70 players already had at least one condition — high blood pressure, waist circumference of 40 inches or greater — that predicted they would be susceptible to heart disease later in life.

"There's no question there are some health risks," said Dan Wathen, longtime athletic trainer at Youngstown State who remembers the day when a 250-pound player was considered huge. "It's manageable when they're playing. It's greater when their playing days are over. If they continue with the same caloric consumption, the health risk is going to go up significantly at that point."

Most of the big players see that day coming. They hear news about Perry — who has been battling a nerve disorder, his weight bouncing between the mid-300s to under 200 at one point, then back up again. And about Newton, who recently had a gastric sleeve put on to shrink the size of his stomach and now bops around at a svelte 250 pounds.

"I keep making a joke around here, I say, 'I'm getting a surgery,'" said Dolphins tackle Vernon Carey, whose weight goes from 335 in season to 360 out of season, talking about his retirement plans.

A notorious victim of fines for being overweight when he played for Jimmy Johnson and the Cowboys in the 1990s, Newton says the biggest he ever got was 411 pounds. He was at an unhealthy 393 pounds as recently as April. Since the surgery, his waist size has gone from 56 inches to 40. Despite the progress, he is still faced with issues most 48-year-old men don't face until later in life.

"I didn't want to die because of fat-related or because I got diabetes or I got high blood pressure," Newton said. "I don't want a heart attack because I'm 400-something pounds. If I die, let it be something else, not something I can do something about."

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AP Sports Writers Alan Robinson in Pittsburgh, Joseph White in Washington, Joe Kay in Cincinnati, Steven Wine in Miami, Teresa Walker in Nashville, Stephen Hawkins in Dallas, Gregg Bell in Seattle, Dennis Waszak in New York, Bob Baum in Phoenix and Pete Iacobelli in Columbia, S.C. contributed to this report.