NASCAR races are raucous, body-shaking events. There's the rumble of dozens of engines, the screaming of delirious fans, as well as the shouting of the announcers. And, just beneath the cacophony, there's a vibration that only the drivers, ensconced in their sleek, powerful machines, with their helmets securely fastened, can feel - the rapid pounding of their hearts.

Driving a racecar is nothing short of exhilarating. Imagine having 750 horsepower at your disposal - at NASCAR races, cars can surpass 200 miles per hour! At such high velocity, drivers must have unwavering concentration and lightning-fast reflexes in order to make steering adjustments to avoid or pass other vehicles, stay in control when making turns, and react to trouble on the track. Inevitably, they experience a stress response, or what's known as the fight-or-flight reaction.

As the term suggests, a fight-or-flight reaction prepares us to deal with a dangerous situation. The hypothalamus, the region of the brain that controls body temperature and other functions, signals the adrenal glands, located above the kidneys, to release a surge of hormones, mainly adrenaline and cortisol. As a result, the heart rate and blood pressure rise. The driver's breathing may be affected. Sweaty palms, dilated pupils, dizziness, and chest pain are also signs of a stress response. Meanwhile, cortisol suppresses the bodily functions that aren't immediately needed to deal with the situation - the digestive system, reproductive system, and growth processes. When the stressful event is over (in this case, the race has ended), the hormone levels fall and the body returns to equilibrium.

While the physical aspect of a stress response can be surprising and uncomfortable, it's a "good" kind of stress that can help drivers perform well. The benefits include heightened energy, concentration, and agility.

Shock is a rather different, and potentially harmful, experience. Modern safety equipment, such as safety belts, driver restraints, and fireproof clothing, save the lives of most drivers involved in accidents, but drivers can still experience shock.

Shock can be caused by trauma, injuries, or blood loss caused by injuries. Blood pressure becomes very low, and as a result the organs do not receive enough blood flow or oxygen. Consequently, cells can die when they are deprived of nourishment, which may lead to permanent damage or even death of the racecar driver.

Symptoms of shock include pale, cold, clammy skin, shallow breathing, vomiting, feelings of faintness or weakness, unusual thirst, and a weak pulse. Drivers may also feel sleepy, lethargic, or confused. In some cases, they feel overly excited or anxious. People in shock can be conscious or unconscious.

At NASCAR and other professional racing events, medical teams are present at the track to aid injured drivers. Of course, shock can happen anywhere to anyone who's been involved in a car accident or experienced a traumatic event. If you have a car accident, even a minor fender bender, and experience symptoms of shock, seek medical help immediately.

If you think someone else is in shock, call 9-1-1 or your local emergency number. While waiting for help to arrive, have the person lie still on his or her back with feet higher than the head, unless raising the legs would injure the person further or cause pain. In this case, have the person lie flat. Keep the person warm and loosen tight clothing. If the person vomits or bleeds from the mouth, turn the person on his or her side to avoid choking. If signs of circulation (breathing, coughing, or movement) are absent, perform CPR.