KINGSLAND, Ga. – Lightning strikes above the live oaks lining the practice field in this coastal town in southeast Georgia. Coach Jeff Herron blows his whistle three times, giving the evacuation orders. A cheer of "Hey!" erupts from the 160 football players as they happily hustle off the field and into the gym.

Coach Herron doesn't share their enthusiasm. A lost practice puts his Camden County High School Wildcats – three-time state champions, in '03, '08, and '09 – even further behind schedule. On Aug. 1, the team was forced to scale back its first full-contact practice due to this year's new statewide heat rules.

"It was on the border," Coach Herron said of that day's weather reading, a complex formula of temperature, humidity and radiant heat. "We were planning on coming out in full pads, but we couldn't do it."

Scaling back the intensity of a football practice due to hot weather was once laughable in South Georgia, where heat, gnats and hard-hitting high school football are facts of life. But this year Georgia became the latest state to enact new rules to prevent heat-related deaths of high school football players, a category in which the state leads the nation.

"The climate's getting warmer so players are exposed to higher temperatures," said Andrew Grundstein, a climatologist at the University of Georgia and a co-author of a 2012 study of heat related deaths in high schools nationwide. Across the country, deaths of high school football players due to heat nearly tripled from 1994 to 2009 compared to the previous 15 years, according to Grundstein's study. Heat illnesses in football players have multiple causes, experts say, but as the climate heats up, practices in Georgia – and around the country – are getting watered down just to be safe.

Lose its punch
Some grumble that South Georgia's trademark football might lose its punch. South Georgia teams have won six of the past nine state championships in Georgia's highest classification. This part of the state is home to the Valdosta Wildcats, the winningest high school football team in the nation, with 869 wins, 23 state and six national championships. Camden County has lost just 15 games in Coach Herron's 13 seasons. This year they join Valdosta in the high school version of college's Southeastern Conference, a region famous for its bruising football and rabid fans.

As Camden's Aug. 25 kickoff in the Georgia Dome nears, the players say that despite a new summer routine – which meant skipping their right-of-passage summer camp – they'll be ready for the season. Coaches, players and parents say that the new heat rules are good, but they'll take some getting used to.

"Certainly it's a step in the right direction. Nobody wants to lose a kid," Herron said.

From 1980 to 2009, 58 high school football players across the nation died from heat-related illnesses, mostly in the month of August, with more than half succumbing during the morning practices when the high humidity can make conditions most oppressive, according to Grundstein and colleagues' study, published in the International Journal of Biometeorology. On average, nearly three players died each year between 1994 and 2009, up from an average of one per year over the previous 15 years. Six players died in Georgia during the study period. Two more have died since.

From 2005 to 2009, there were 18 exertional heat stroke deaths among football players nationwide, with all but one at the high school level. That's the most in any five-year block over the past 35 years, and twice the five-year average, according to the University of Connecticut's Korey Stringer Institute, which studies heat stress in sport and is named after the Minnesota Vikings offensive lineman who died from exertional heat stroke in 2001.

Kids' lifestyles
The ten warmest consecutive 12-month periods in recorded history for the United States have occurred since 2000, according to the U.S. National Oceanic and Atmospheric Administration. August 2011 to July 2012 was the warmest 12-month period that the contiguous United States has ever experienced; July registered as the warmest month the nation has ever seen, eclipsing a record set in the Dust Bowl, according to NOAA.

Might there come a time when the climate in the South is just too oppressive for summer football workouts?

"I think you can do it safely, but you have to really monitor," Grundstein said. "I do think it's really important to have a policy in place because you're only going to get more days that are really oppressive."

Coach Herron, however, says the real problem today isn't the heat, but the kids' lifestyles.

"It's not any different," Herron said of the heat these days. "The difference is that when we were kids, we were out playing all summer. We were outside, we weren't laying in the air conditioning."

So that kids don't jump from the air conditioning into the oven, Georgia's new heat rules require an acclimatization period of five days – practice in helmets only – before players are allowed to suit up in full pads on Aug. 1.

Georgia's rules were based on a study by athletic trainers at the University of Georgia, who presented their unpublished work at the annual meeting of the National Athletic Trainers' Association last summer and to the Georgia High School Association's football subcommittee in January.

The researchers say they found that the first weeks of preseason practice are when the risk of heat related illness is greatest.

To lessen the risk, Georgia's high school football overseers this year adopted heat guidelines similar to those published by the National Athletic Trainers' Association [PDF] in 2009. Three-a-day practices are now banned. Teams cannot have two practices per day on consecutive days. Because many teams lift weights in tin sheds that lack air conditioning, weight training now counts as practice time.

Every team in Georgia is now required to have a "wet bulb globe temperature" meter on the practice field. The metric incorporates air temperature, humidity and radiant temperature. The reading tells the athletic trainer or coach what the weather feels like down on the field; if the reading passes certain cutoff points, practices must be shortened or equipment shed.

"The more equipment that you have on, the body's ability to remain in a cool, safe temperature becomes impacted," said athletic trainer Bud Cooper of the University of Georgia and a study co-author. "As that (wet bulb globe temperature) goes higher and higher, in order to allow the athlete to continue to participate, modifications need to be made to allow him to stay cool."

At a wet bulb globe temperature reading of 92, equivalent to a heat index of about 105, outdoor practice must be cancelled.

No helmets or pads
Before Georgia's heat rules began, the Marietta High School Blue Devils in metro Atlanta, one of the teams studied by Cooper and colleagues, practiced under stricter standards than the state now requires. For years, they used a wet bulb globe temperature reading of 88 as their cut-off point for practice. But by using flexible practice times and creative practice schemes, they never missed a practice, said Marietta High's athletic trainer Jeff Hopp, who is also president of the Georgia Athletic Trainers' Association.

Marietta's coaches often shift practices to the evening to avoid the intense afternoon heat. Or the players often take the field in helmets and football pants, leaving their shoulder pads on the sideline. As the wet bulb globe temperature reading falls, they'll strap on their shoulder pads for full contact practice. A 2007 study by Georgia Tech found that taking shoulder pads off helps the body keep its core cool.

"We were working with stricter guidelines before and we never cancelled a practice," Hopp said. And that's not because players in the northern half of the state have an easier climate for practice, Hopp said. "When you're looking at the wet bulb globe temperature, across the state it only varies by a couple of degrees."

Since 2003, the National Collegiate Athletic Association has operated under rules similar to those now in place in Georgia. Players not only had fewer cases of exertional heat illnesses, but their orthopedic injury rate also improved.

"It's been a real positive on the collegiate level," said Michael Ferrara, an athletic trainer at the University of Georgia and co-author of the study that informed Georgia's heat rules. "Our guess is the same thing is going to happen on the high school level, that you're going to see a reduction in the number of injuries around this preseason period, ... and still go forward with a great football season."

Including Georgia, seven states have adopted heat safety standards similar to the NCAA and NFL: Arkansas, Arizona, Connecticut, North Carolina, New Jersey and Texas, according to the Koery Stringer Institute.

A quick knee and a swig of water
To see how the risk of heat-related illnesses will change under Georgia's new rules, the GHSA has agreed to fund Cooper and Ferrara's research for three additional years.

"We need to be really careful that we don't assume that even with all the safeguards and precautions that followed, that we're going to avoid any instances of heat illness," said GHSA Executive Director Ralph Swearngin. "What we are hoping is that we will keep them at a minor level because we're aware of what to look for."

At Camden County High School, the beginning of the Aug. 2 practice looked more like a chaotic dance rehearsal, except for the large lineman crawling to the center of the field, sans hands, because he was late for practice. There was little contact, though the players were in full pads. Linemen, however, practiced their footwork without helmets during one drill. Players took breaks nearly every 10 minutes. Some breaks were brief, just a quick knee and a swig of water. For longer breaks, players huddled under shade.

Then the hitting began. A chorus of barking coaches rose and fell with each jarring collision. Dozens of parents in the parking lot formed an unblinking audience. Water was available as players rotated in and out of the huddle. Helmets did not come off.

The players are concerned about getting enough reps, but they're confident they'll be ready, even as they prepare to play a team from Florida that doesn't play by the same heat rules.

"I feel like it kind of set us back," said Brice Ramsey, the team's senior quarterback, who has committed to play college football at the University of Georgia. "Over the summers the last couple of years we were in shoulder pads and going to camps and stuff. This year we had to wear no pads and weren't in helmets half the time."

Senior fullback Jaccob Johnson said that, to make up, "we're just practicing harder, going at everything 100 percent and trying our best."

That drive to shine under the Friday night lights is so powerful that some players put in overtime, never mind the heat and humidity. The heat rules apply only to coach supervised practice. What players do on their own time is unregulated.

As the parking lot thinned after the Wildcats' first practice in full pads, senior wide receiver and defensive back Antwaun Lewis was still on the field, running sprints alone, as evening faded to night.

As he jogged off the field, shoulder pads and helmet in hand and sweat dripping from his face, he explained his motivation: "Just trying to be better than the next man."

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This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.