Alex Brandon, Associated Press
Philadelphia Eagles head trainer Rick Burkholder updates the media on the condition of defensive tackle Mike Patterson who had a seizure during NFL football training camp at Lehigh University Wednesday, Aug. 3, 2011 in Bethlehem, Pa.

PHILADELPHIA — When an ambulance carrying Eagles defensive tackle Mike Patterson to a hospital pulled away from the team's practice field Wednesday morning, it served as a grim reminder of the hazards of training camp.

Patterson was in stable condition after suffering a seizure during Philadelphia's practice, head athletic trainer Rick Burkholder said. It was unknown why Patterson collapsed, and he was expected to stay overnight at the hospital for observation and further tests.

NFL teams have been cautious about preventing heat-related illnesses, especially after Minnesota's Korey Stringer collapsed and died from a heat stroke at Vikings training camp in 2001. It was a cool day at the Eagles' camp at Lehigh University. The temperature was in the high 70s when the team began its morning session.

"We are not going to speculate that's what it is, but you can have a seizure due to dehydration," Burkholder said. "I don't want to speculate that it's heat, but I've sat up here before and talked about dehydration. That's an ongoing event, day after day, your tank can empty slowly and it can catch up to you."

Patterson collapsed and dropped to the ground between plays during morning drills, and then began violently shaking. Burkholder said the seizure lasted about four minutes, and Patterson lost consciousness at one point as he was on the ground.

The incident shook up Patterson's teammates. Players kneeled nearby, holding hands and praying, as Patterson was placed on a stretcher and lifted into the ambulance.

"My thoughts and prayers are going to be with him tonight," said rookie lineman Danny Watkins, a trained firefighter who tried to assist Patterson.

Patterson texted teammates to let them know he was fine.

While it's unknown whether heat or dehydration played a role in Patterson's case, teams are being extra careful this summer, especially since the NFL lockout canceled organized team activities and minicamps.

The Vikings are one of the teams that test players' urine for hydration, give them a pill that helps monitor core temperatures and keep Gatorade and water all over the facility for easy access. But the lockout made it tougher on the team's training staff to evaluate rookies and other new players, learn who has issues with cramping and educate them on the importance of hydration.

"One of the things we've talked about is that it takes your body 10-14 days to acclimatize," Vikings head athletic trainer Eric Sugarman said. "If you haven't been working out in the heat and now all of a sudden we want to go for a run today, and we haven't done it in hot weather, we're going to have a hard time. And it's going to take us a week to 10 days to adapt to that."

Most teams have eased into their practice routine at camp, and free agents haven't been allowed to participate yet. Under the new collective bargaining agreement, there are fewer practice sessions and less hitting.

The lockout forced players to prepare on their own during the offseason. Some hired personal trainers and worked out with teammates. Others did nothing. Those who arrived to camp out of shape are at a significant disadvantage.

Steve Saunders, CEO of Power Train Sports Institute, trained more than 35 Eagles players at one of his gyms in Cherry Hill, N.J. Patterson, who lives in California during the offseason, wasn't among them.

"The guys that have been disciplined and faithful with all their stuff are going to be way ahead of the game," Saunders said. "Will they still be hot when it's 100 degrees out? Yeah. Will they still get tired? Yeah. But those guys are light years ahead of the guys that haven't been doing much or the ones who think they can show up and get in shape in camp. Those guys will be so far behind and they might not know it until September, October."

The Vikings cut former Pro Bowl left tackle Bryant McKinnie on Tuesday because he showed up to camp overweight and out of shape.

"With so much time off, guys do different things," Vikings cornerback Antoine Winfield said. "Some guys relax, some guys travel, some guys like to party. But you have to be disciplined. All you have to do is go work out, stay in some kind of shape and come in here and perform."

Young players are not only adjusting to life as pros, but they've got to be ready for preseason games after less than two weeks of practice.

"The crazy thing is down in Florida State in college, you practice four or five weeks before you have a game," Vikings rookie quarterback Christian Ponder said.

Different teams have various ways of monitoring their players. The Dolphins added several cold tubs that hold up to three players. The tubs are filled with ice and water, and players jump in after practice to cool off. They've also added more breaks during practice to allow players to hydrate and they now weigh guys before and after sessions.

"We have a three-minute break between periods to give guys a chance to recover," Miami linebacker Karlos Dansby said in Davie, Fla.. "It has been working. It definitely saved us today because it was a scorcher. I think it was 120 on the field. This was the hottest day ever. You've got to prepare and recover and try to get ready for this heat. We've got to attack it. Like Coach says, you can't be scared of the heat. You've got to fight through and continue to practice hard."

Through five practices, the Colts have not worn pads and they've been taking regular water breaks.

"It's kind of like in the college days," Colts coach Jim Caldwell said. "You always had three days of shorts only, to sort of acclimate them to the weather, to get running soreness out so you can adapt and be just as fast without pads as in them."