Tips for runners: What happens to your body during a race

• Don't arrive until about an hour before your time group is scheduled to start. Heat is a runner's worst enemy on July 4, and coming later will keep you from waiting in the sun.

During

• Self-awareness is key. Many runners — especially younger, more competitive participants —won't notice signs that they're pushing too hard, until they collapse. "This is not the time to run your personal best or accomplish the time you got five or 10 years ago," Wilson said. "The physiological risks to your health are too great."

• Watch for the early symptoms of a heat-related illness: dizziness, lightheadedness or unsteadiness, headache, nausea, chills and goose bumps.

• Keep cool by running through the water sprays on the course, dumping cups of water over your head and grabbing more at water stations, located every mile of the course on both sides of the street.

After

• Cool down. Drink water, stand in front of a fan. Most Peachtree health problems are heat related.

• Treat any blisters or scrapes you've gotten along the way. A "walking wounded" station at the end of the race will handle non-life threatening race injuries.

• If something seems unusually painful, check with doctors and medical volunteers at the end of the race. They can advise runners on whether a trip to the emergency room is necessary.

• Most common post-race complaint: headaches, usually caused by dehydration. "Ask yourself, 'Have I been passing any urine?'" Wilson said. "If the answer is no, you're way behind."

• Runners who aren't well conditioned often wake up sore on July 5. Get out and walk, and keep doing it —right up until next year's race. "This is advice for people not taking the advice on the front end," Wilson said.

Every year, the AJC Peachtree Road Race brings together 55,000 runners from amateurs to professionals, well-conditioned to just-started.

Medical volunteers, paramedics on bikes and doctors are on hand to help injured or ill people, but it helps to understand what the body is going through during a 10K.

Here's an explanation from Wilson.

Brain

Blood flow to the brain is maintained in almost all circumstances, including running, but it is temperature sensitive.

Peachtree runners are likely to have body temperatures around 100. Temps of 103 are when problems really start to arise.

Wilson advises runners to keep their temperatures under control by running at a comfortable pace, rather than ignoring the body's signals that it's pushing too hard.

Heart

The heart works harder to get oxygen and other chemicals to muscles while running. For someone trying to run without conditioning, it might be like an intense softball game or long stretch of yard work.

If you have a family history of heart trouble, recent chest pains, high blood pressure or cholesterol, it's best to check with a doctor before you run in a 10K.

Muscles

Some muscles will contract and relax more often than usual on race day. Runners need to keep them filled with oxygen and nutrition for them to operate. Runners should eat a light breakfast before the race. Just as important: keep breathing. (It doesn't always come naturally to people focused on a finish line.)

Skin

Runners should expect to sweat a lot during the race as the body tries to cool down. What really brings temps down, though, is the evaporation of liquid from the skin. Wear appropriate clothing, stand in front of fans and stay hydrated.

Women typically have larger layers of subcutaneous fat, which acts as another layer of insulation and a barrier to cooling down.

Blood

You're running, you're hot and your heart is having to pump more blood toward your skin to keep you cool. During a race, other body parts will actually see less blood flow, like your stomach and intestinal tract, and food eaten just before or after a race isn't able to digest as it normally would.