Early Pregnancy And Exercise

Travel Across Time Zones

The synchronization of many biological rhythms is generally believed to be beneficial for survival, because a coordination of circadian rhythms enhances biological function, and b organisms experience natural changes in electromagnetic fields, light, temperature, humidity, and air pressure regularly. Also, daily, monthly, and yearly rhythms are believed to be beneficial because it is more economical to be programmed to anticipate the cyclic demands of environmental synchronizer signals than to rely on immediate responses to one set of environmental conditions that is repeated every day and another set that is repeated every night.

Travel across time zones severely desynchronizes biological rhythms.

The significance of coordinating biological rhythms is summarized by Ehret and colleagues:

A creature with all its systems in strong synchrony somehow learned how to put it all together..Such fortunate creatures are rewarded by functional proficiency and longevity. The opposite is true, as well. When you experience environmental, social, psychological, industrial, or athletic stressors that subtly disrupt biological rhythms, you become less efficient and effective because the systems of your body are not coordinated. A basic principle of chronobiology states that internal synchronization of biological rhythms is critical to good health and well-being. In contrast, research suggests that desynchronization of circadian rhythms can have detrimental effects on physical and mental performance. It is even possible that desynchronization of annual rhythms results in some of the mental disorders that have been associated with the change of seasons seasonal affective disorder. It is noteworthy that humans are the only species that regularly choose a lifestyle that leads to a disruption of the phasing of internal rhythms.

Rapid travel across time zones latitudinal or transmeridian air travel provides one of the most potent desynchronizing agents known to science. The change in light-dark cycles and training/work schedules can modify virtually any biological rhythm, and results in what is commonly known as jet lag. This condition results when internal circadian rhythms entrained to the time zone of departure are out of synch with environmental cues at the time zone of arrival. Imagine the desynchronization that astronauts experience, as they are exposed to light and dark changes several times during each period!

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When an athlete travels from the East Coast to the West Coast of the United States, are added to the length of his or her day, delaying normal circadian rhythms. However, each day that this athlete resides on the West Coast, the cycles of body temperature and other physiological variables shift approximately per day. Although these circadian rhythms eventually match the zeitgebers of the new time zone, after several days, it is difficult to adapt to transmeridian travel that involves a difference of more than five time zones. In this case, at least days should be allowed for resynchronization. In contrast, following an eastward flight, a traveler adapts to the new time zone by advances in biological rhythms. In this instance, body temperature and other cycles reach their peaks and valleys approximately earlier each day. This likely explains why travelers report that flights from west to east shortened day disturb circadian rhythms more than flights from east to west lengthened day. Adaptation is faster after westbound travel because the days are longer. For example, during an jet flight from New York to Los Angeles, the amount of daylight experienced is going west but only going east, if sunrise and sunset occur at : A.M. and : P.M. respectively. North to south, and south to north, flights have little impact on circadian rhythms.

Athletes may require to days to recover from international, transmeridian travel. The U.S. Olympic Committee recognized this prior to the Summer Olympic Games in Seoul, Korea. Seoul lies seven time zones from Los Angeles and ten from New York. The USOC prepared a brochure titled From the U.S. to SeoulHow to Avoid Jet Lag, which included guidelines to help athletes avoid desynchronization of biological rhythms. Tablepresents estimates of the number of days required to fully resynchronize various circadian rhythms after air travel that involves west to east flights spanning six to nine time zones. This information was gleaned from three reputable sources. Clearly, resynchronization does not occur rapidly.

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