Your body's reaction to fear, stress, excitement and anxiety is a result of the instinctive fight-or-flight response. Our bodies involuntarily react to dangerous situations through the sympathetic nervous system. Several responses in various parts of the body prepare us to deal with possibly life-threatening, or sometimes just scary, situations.
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The sympathetic nervous system is part of the autonomic nervous system. The other part is the parasympathetic nervous system. These two parts serve opposing purposes. The parasympathetic nervous system relaxes the body; the sympathetic nervous system prepares the body for fight or flight. This response is hard-wired in humans to protect us against threats from predators and other aggressors. Your body prepares itself to fight or flee in the face of perceived danger.
In modern America, life-threatening situations are rare, but the body still reacts to perceived threats -- such as scary, adrenaline-pumping roller coasters. The sympathetic nervous system has a number of potential responses to help you in a stressful situation. The usual responses are increases in heart rate, blood pressure, respiration and blood sugar. These responses pump more blood to the brain and muscles so you can react quickly and decisively.
A study published in the "Journal of the American Medical Association" measured the heart rate responses of 55 healthy men and women on a roller coaster. The participants all wore 12-lead Holter electrocardiogram recorders, starting five minutes before the ride and ending five minutes after the ride. The average increase was from 89 beats per minute before the ride to 155 beats per minute during the ride. The largest increase occurred during the initial ascent. Because this part of the ride is at low speed and there are no acceleration forces, researchers theorize the increase was caused by the body's natural response to fear or emotional stress with the fight-or-flight response.
The study noted that 24 of the participants experienced asymptomatic sinus arrhythmias, or irregular changes in the heart rhythm. The researchers determined that because of the intense heart responses of riding a roller coaster, individuals with heart conditions should stay away from these thrill rides. However, not all doctors and organizations agree with this absolute. The American Heart Association simply advises individuals with heart conditions to consult with their physicians prior to riding a roller coaster.