单选题
Set Your Body's Time Clock
Our Body Operates Like a Clock A. As the first rays of sunlight filter over the hills of California's Silicon Valley, Charles Winget opens his eyes. It is barely 5a.m., but Winget is
raring (渴望) to go. Meanwhile, his wife pulls up the covers and buries her face under the pillow. 'For the past fifteen years,' says Winget, 'We've hardly ever gotten up together.'
B. The Wingets' situation is not uncommon. Our bodies operate with the complexity of clocks, and like clocks, we all run at slightly different speeds. Winget is a morning person. His wife is not at her best until after nightfall.
C. Behavioral scientists long attributed such differences to personal eccentricities or early conditioning. This thinking was challenged in the late 1950s by a theory labeled chronobiology by physician-biologist Franz Halberg. In a Harvard University laboratory, Dr. Halberg found that certain blood cells varied predictably in number, depending on the time of day they were drawn from the body. The cell count was higher at a given time of day and lower 12 hours later. He also discovered that the same patterns could be detected in heart and metabolic rates and body temperature.
D. Halberg's explanation: instead of performing at a steady, unchanging rate, our systems function on an approximately 25-hour cycle. Sometimes we are accelerating, sometimes slowing down. We achieve peak efficiency for only a limited time each day. Halberg dubbed these bodily cadences 'circadian rhythms'.
E. Much of the leading work in chronobiology is sponsored today by the National Aeronautics and Space Administration. Charles Winger, a NASA research physiologist and authority on circadian rhythms, says that circadian principles have been applied to astronauts' work schedules on most of the space-shuttle flights.
F. The space-age research has many useful applications here on earth. Chronobiologists can tell you when to eat and still lose weight, what time of day you're best equipped to handle the toughest challenges, when to go to the dentist with your highest threshold of pain and when to exercise for maximum effect. Says Winget, 'It's a biological law of human efficiency: to achieve your best with the least effort, you have to coordinate the demands of your activities with your biological capacities.'
How to Figure Out Your Body's Patterns G. Circadian patterns can be made to work for you. But you must first learn how to recognize them. Winger and his associates have developed the following approach to help you figure out your body's patterns.
H. Take your temperature one hour after getting up in the morning and then again at four-hour intervals throughout the day. Schedule your last reading as close to bedtime as possible. You should have five readings by the end of the day.
I. Now add your first, third and fifth readings and record this total. Then add your second and fourth readings and subtract this figure from the first total. That number will be an estimate of your body temperature in the middle of the night—consider it your sixth reading.
J. Now plot all six readings on graph paper. The variations may seem
minuscule (极小的)—only one-tenth of a degree in some cases—but they are significant. You'll probably find that your temperature will begin to rise between 3 a.m. and 6 a.m., reaching a peak sometime in the late morning or early afternoon. By evening the readings start to drop. They will steadily decline, reaching their
nadir (最低点) at around 2 a.m.
Learn to Use Your Body's Pattern K. Of course, individual variations make all the difference. At what hour is your body temperature on the rise? When does it reach its highest point? Its lowest? Once you have familiarized yourself with you patterns, you can take advantage of chronobiology techniques to improve your health and productivity.
L. We do our best physical work when our rhythms are at their peak. In most people, this peak lasts about four hours. Schedule your most
taxing (费力的) activities when your temperature is highest.
M. For mental activities, the timetable is more complicated. Precision tasks, such as mathematical work are best tackled when your temperature is on the rise. For most people, this is at 8 or 9 a.m. By contrast reading and reflection are better pursued between 2 and 4 p.m., the time when body temperature usually begins to fall.
N. Breakfast should be your largest meal of the day for effective dieting. Calories burn faster one hour after we wake up than they do in the evening. During a six-year research project known as the Army Diet Study, Dr. Halberg, chronobiologist Robert Sothern and research associate Erna Halberg monitored the food intake of two groups of men and women. Both ate only one 2000-calorie meal a day, but one group ate their meal at breakfast and the other at dinner. 'All the subjects lost weight eating breakfast,' states Sothern. 'Those who ate dinner either maintained or gained weight.'
O. If foods are processed differently at different times of day, certainly caffeine, alcohol and medicines will be too. Aspirin compounds, for example, have the greatest
potency (力量) in the morning, between 7 and 8. (So does alcohol.) They are least effective between 6 p.m. and midnight. Caffeine has the most impact around 3 in the afternoon. Charles Walker, dean of the College of Pharmacy at Florida A & M University, explains, 'Stimulants are most effective when you are normally active, and
sedatives (镇静物) work best when you're naturally sedate or asleep.'
P. Knowing your rhythms can also help overcome sleep problems. Consult your body-temperature chart. Your bedtime should coincide with the point at which your temperature is lowest. This is between 11 p.m. and 2 a.m. for most people.
Q. Dr. Michael Thorpy of the Sleep-Wake Disorders Center at Montefiore Medical Center in New York City offers other circadian sleep tips: go to bed at the same time every night and get up at the same time every morning, even on weekends. 'Irregularity in sleep and waking times is the greatest cause of sleep problems,' Dr. Thorpy says. The best way to recover from a bad night's sleep is simply to resume your normal cycle. Beware of sleeping pills. 'Most sleeping pills won't work for periods longer than two weeks,' warns Dr. Thorpy. And there is real danger of drug accumulation in the blood.
R. Visit a doctor or dentist as early in the day or as late in the evening as possible, since your highest pain threshold is between 8 p.m. and 8 a.m.
S. Winget and fellow NASA chronobiologist Charles DeRoshia also offer advice to diminish the debilitating effects of jet lag: a week or so before departure begin adjusting your daily activities so that they coincide with the time schedule of your destination. Eat a small, high-protein, low-carbohydrate meal just before your trip. Get plenty of sleep in the days before your trip. In flight, eat very little, drink lots of water and avoid alcohol and caffeinated drinks. When you arrive, walk around, talk to people, try to adapt to your environment. Before retiring, have a light meal, high in carbohydrates. Take a warm bath.
T. Knowing your body's patterns is no guarantee of good health. But what chronobiology reveals is the importance of regularity in all aspects of your life and of learning to act in synchronization with your body's natural rhythms.