On a clammy May morning in Greenboro, N.C., Chad Wiley ran up a steep hill with fellow North Carolina A&T State University football team members. The last of the morning coolness had given way to intense humidity, and the pre-season conditioning session was almost over. Just a few minutes later, as he and his teammates walked back to the training room, Wiley collapsed and passed out. He was pronounced dead about an hour later.

An autopsy later revealed that Wiley died of complications from a heatstroke and sickle-cell trait, a condition associated with sudden deaths. Wiley, who died in 2008, is one of 21 college football players who have collapsed and died during pre-season workouts since 2004-many during the first few days of practice, when coaches push even the fittest players too hard.

In an effort to make pre-season conditioning just as safe as in-season play, health and sports professionals have collaborated to create the first consensus guidelines on preventing sudden deaths in workouts.

Minimal or no regulations are placed over pre-season conditioning, and coaches "just run willy-nilly," trying to make men out of boys, said Douglas Casa, athletic director and trainer at the University of Connecticut. "A lot of them are not focused on health and safety issues."

Pre-season workouts often include running sprints, lifting weights, and repeated endurance drills. Once the season begins, practices and games have much more oversight and safeguards, including heat acclimatization rules limiting the equipment players can wear and the intensity and number of sessions for summer practices, depending on the sport.

Casa, who helped draft the new guidelines, believes the same recommendations are good advice for high schools and younger athletes too. The guidelines will prevent deaths and keep players safe at every stage in every sport, he said.

The football conditioning deaths "generally occurred with excessive exercise under the direction of a coach, often in extreme conditions, and in some cases with staff unprepared to deal with the emergency in a timely or appropriate fashion," said Jolie Holschen, a Chicago emergency medicine and sports medicine specialist who co-authored the new guidelines.

Heat stroke, heart conditions and the genetic trait related to sickle cell anemia, which has effected 10 athletes who died, made up the most common causes of the 21 NCAA deaths. In normal conditions, sickle cell anemia doesn't cause problems, but athletes with the trait who workout too hard can disrupt the blood's ability to carry oxygen to muscles, which can be deadly.

Ten percent of black athletes carry the trait. Smaller numbers of whites and Hispanics have it too.

U.S. infants are tested for the trait at birth, and in 2012, the NCAA began requiring blood tests for it in Division I, after Rice University player Dayle Lloyd II died during a preseason workout in 2006. Blood Tests for Division II athletes took effect this year.

According to the new recommendations, conditioning workouts should gradually build up to maximum intensity over a period of time, instead of pushing athletes to their limits on day one.

Conditioning coaches should be trained in health and safety issues; certified in first aid, resuscitation and heart defibrillation; know which athletes have the sickle cell trait; and know how to recognize signs and treat exercise-related complications from the condition.

The guidelines challenge "the old athletic mentality that if a little bit is good, a lot must be better," said Jim Thornton, president of the trainers' association and head athletic trainer at Clarion University, in Clarion, Pa.

Thornton is excited about the new regulations and believes they will expose gaps that need to be filled in the high school sports as well as collegiate athletics. Finding a high school with an athletic trainer can be difficult and practices for most sports take place without anyone trained in first-aid present.

Of the injuries cited, many involve a muscle-damaging condition called exertional rhabdomyolysis, rhabdo for short. Intense exertion can cause muscle cells to leak enzymes and protein into the blood. Symptoms include extreme muscle pain and dark urine. Severe cases can lead to kidney failure and sudden death.

Reported cases include 13 University of Iowa football players hospitalized last year after a too-strenuous, off-season weight-lifting session, and 12 Oregon high school football players treated in 2010 after an intense preseason workout.

The recommendations were released June 27 at the National Athletic Trainers Association annual meeting in St. Louis.

"We're supportive of the effort to address these issues that they raise," said David Klossner, the NCAA's director of health safety.

The Associated Press Contributed to this report.