A small plaque lies before a tree planted in Korey Stringer's (search) memory at Minnesota Vikings training camp. "In Memory of Big K," it reads, honoring the beloved right tackle who died four years ago from heatstroke (search).

There was no way for trainers to monitor players' core temperatures on that sweltering July day when Stringer collapsed, no definitive way to tell that his massive body was overheating beyond its threshold.

But now there is, in the form of a swallowed capsule that measures core body temperature as it passes through the digestive system, and the Vikings — along with a few other NFL teams — are using it.

The Core Temp Ingestible Core Body Temperature Sensor (search) was developed in the late 1980s by HQ Inc., of Palmetto, Fla., as a research tool used for a number of projects, including monitoring how certain pharmaceutical drugs affect the body's core temperature.

The pill has evolved in the past couple of years or so into a protective device for athletes — in football, tennis, running and other sports — who train in intense heat, according to marketing director Susan Smith.

The Vikings, Jacksonville Jaguars and Philadelphia Eagles are using the device to gauge the effect of suffocating heat on huge athletes going through intense August workouts in pads and a helmet. Without the pill, monitoring is anything but an exact science.

"We've had some people get to 106 degrees and not have symptoms and some get to 102 and have symptoms," said Rick Burkholder, head athletic trainer for the Eagles. "Some guys' core temperature rises after they come off the field and stand around and other guys, it goes down when they come out. It depends on the individual."

Such was the case in Mankato on July 31, 2001, with the 335-pound Stringer. The heat index soared to 110 degrees on that day, the hottest day of the year in Minnesota.

Stringer had left practice early the day before. Determined to stick this one out, he labored during his final practice, but didn't summon a trainer until the session was over.

Head coach Mike Tice, who was offensive line coach at the time, said Stringer never showed any symptoms of heat illness.

"He didn't look like he needed water," Tice said then. "He looked good on film, too. He had a fantastic practice. He was sharp. He was crisp. He got all his blocks."

About 15 hours later, Stringer died at a nearby hospital, his body temperature over 108 degrees. The loss of an immensely popular teammate remains with the Vikings to this day.

"It's still vivid in my mind," center Cory Withrow said. "I can still picture that whole day."

Pat Williams was playing for the Buffalo Bills when Stringer died. The news certainly hit home with the rotund nose tackle, who is listed generously at 317 pounds.

"Wow," was all Williams could say when asked to recall his reaction. "I started eating better, started watching my weight, anything I could do to keep me safe."

Now with the Vikings, Williams is one of about two dozen players on the team who take the pill, which costs around $30 each, every day before practice.

Team trainers come up behind him periodically throughout the day and hold an electronic sensor close to his back. The pill transmits a core temperature reading and allows trainers to decide when the player needs to pull back and cool down.

It also gives Williams some valuable peace of mind, even if he is used to working out in extreme heat in his native Louisiana.

"Everything will be all right, yep," Williams said confidently. "I'm from down South. You probably need to take two of those pills if you're working out down there, but it's good to have."

Vikings trainer Chuck Barta is elated to have another tool to help keep players safe. He said there are certain factors the trainers look at before asking a player to take the pill, which stays in the system for about 24 hours.

"There's certainly variables you look at, the biggest being past history," Barta said. "If they've had problems in the past, the bigger guys, those are the ones we'd like to participate."

After treating three players for heat illness during training camp in 2003, Jaguars head trainer Mike Ryan takes a similar approach.

"We have what we call a 'watch list.' It's usually for the larger players or players who have a history of conditioning factor or anyone who's lost a lot of weight just before camp," Ryan said.

Ryan said if the pill is working properly, it all but eliminates the risk of another heatstroke death.

"If it works and it's doing it's job, no one will get to the stage where there's a problem," Ryan said. "That's what we like. It's a form of preventative medicine."

That's exactly what Tice wants to hear. The coach was very close to Stringer, and said at the time that he hoped the hole left in his heart from Stringer's absence never heals.

"Yes, I think it's a good thing," said Tice, who wears a long-sleeve shirt at practice — even on the hottest days — so he can gauge the heat for himself. "If what we think about the heat is true, we're very on top of it. ... Certainly we want to make sure that we monitor it every step of the way."

Now every team is conscious of what can happen when large men are pushed too hard in searing heat. But it undoubtedly resonates on the Minnesota State University campus just a little more.

"There's always going to be a heightened sense of awareness going forward since Korey's loss so they probably take it more seriously here," guard Chris Liwienski said. "It's something that's in the back of my mind and we'll never stop thinking about. It's a tragedy we all had to live through and there's always going to be a place in my heart for him."