THE best times to eat, sleep, work, do mental work and to have sex are all set out like clockwork in traditional Chinese medicine. Zhang Qian counts the hours.

There's a time for everything in traditional Chinese medicine, and timing and schedule are crucial to maintain health.

Our bodies move like clockwork and each organ meridian has a two-hour period when qi (energy) is at its peak.

The qi flows clockwise through the 12 meridians over 24 hours and shifts between yin (cold) and yang (hot) energies.

Living according to the clock can strengthen health. Small practices, such as walking and massage, can help achieve a healthy schedule.

Back in the Warring States Period (476-221 BC), the earliest foundational text of Chinese traditional medicine, "Medical Classic of the Yellow Emperor," sets out a guide to healthy living, not by prescribing medicine, but a way of life in tune with the universe and the body's rhythms and cycles. That includes deep sleep.

Chinese recognize 12 two-hour time units in a day the "12 earthly branches" - zi, chou, yin, mao, chen, si, wu, wei, shen, you, xu and hai.

In a day, the 12 meridians are rivers of energy that carry qi through our bodies and the organ functions best when energy is focused there. Completing the activity, such as eating, at the right time, ensures that energy flows properly and the digestive system works at its best.

Disrupted energy flow leads to health problems.

Chou (1-3am) and yin (3-5am)

People should be in deep asleep during both chou and yin. The liver meridian is on duty at chou to dispel toxins and produce fresh new blood in liver, while lung meridian is on duty at yin to distribute the energy and blood produced by the liver to the organs. Both jobs can best be accomplished while people are fast asleep.

People who are restless and suffer insomnia may have over-active yang energy.

Exercises are recommended at that time to help soothe nerves and dispel overactive "fire" in the organs, said Dr Wang Wenjian of the internal medicine department at the Shanghai Chinese Clinic and Medicine House.

One should sit in bed with warm clothes around the shoulders. Take one or two deep breaths and exhale to get rid of foul qi. Rub the hands together until they are warm, then rub the wings of the nose around 35 times while covering the eyes with a warm palm. Move the ears back and forth 35 times; cover the ears with the hands, leaving fingers at the back of the head; pound the back of the head with middle fingers 25 times. Stretch arms wide at each side. Swallow saliva three times, imaging it flowing down to the navel. Try to go to sleep.

Mao (5-7am)

When the lung meridian finishes its job of distributing energy and blood to the organs from 3am to 5am, the large intestine takes over. This means one should get up, go to the toilet and move the bowels at this time. Wear appropriate clothes so guard against invading pathogenic energies.

In addition to answering nature's call, during these two hours one should sit next to a window in the light, drink a cup of warm water rather than tea and comb the hair and head repeatedly. This helps dispel pathogenic energies in the body and clear the eyesight and the mind. Time to wash.

Chen (7am-9am)

Now it's time for breakfast at chen since the stomach meridian is active. Eat warm foods, such as congee, take a little rest and take 50-60 steps slowly. Rubbing the stomach and belly while walking helps improve digestion.

With sufficient yang energy from food, the spleen then turns the nutrition into energy and leaves no extra fat to accumulate (if one doesn't overeat at breakfast).

Si (9am-11am)

Blood and energy flow to the spleen meridian at si to support metabolism, conversion of nutrients into blood and energy and send them to muscles. These two hours are prime time for working since healthy spleen can finish the job. And the energy and blood distributed by the spleen will support activity.

Wu (11am-1pm)

Lunchtime. A balanced, nutritious lunch is important. It should be warm and filling and should not contain raw or hard foods, according to Dr Wang. Lunch shouldn't be too big. Take a slow walk after lunch and rub the stomach and lower back to get the spleen and kidney active. Drinking a little tea and taking a half hour's nap is recommended.

Wei (1pm-3pm)

After lunch and a nap (no more than an hour), it is time for more activity, as the small intestine works to separate and distribute digested nutrients.

Shen (3pm-5pm)

These are prime hours of the day for work and study. It's when the bladder meridian goes to work. There are two bladder meridians, one on each side of the spine and running from foot to the head and the brain. Since energy and blood flow actively into the brain during shen, it is a good time for efficient work.

Drinking afternoon tea is advised. The bladder meridian also is a major toxin-expelling channel and handles toxins dispelled by other meridians. Drinking extra water promotes detoxification as toxins are passed in urine.

You (5pm-7pm)

The kidneys start to store "essence" as the kidney meridian takes its turn. This is the best time for kidney-reinforcing therapy.

It's time for dinner but not too much. A little wine is good to activate blood circulation, according to Dr Wang, but don't get drunk.

Wu (7pm-9pm)

The pericardium is the fluid-filled sac that surrounds the heart and the roots of the major blood vessels. It contains channels of blood and energy. When it is activated at wu, it dispels all the pathogenic energy around the heart to protect it.

At this time it's advised to soak the feet in hot water, which can help dispel pathogenic heat and damp and activate the blood.

This is a good time for a bit of reading, says Dr Wang, but not too much lest it hurt the eyes. It's also not advisable to "think" too deeply at wu, since too much mental activity causes excessive fire-heat ascending and deficient kidney yin, resulting in heart-kidney imbalance and possible sexual dysfunction. Massaging yong quan point (the arch of foot) in both feet can help nourish kidney energy.

Hai (9pm-11pm) and zi (11pm-1am)

Zi is the darkest hour when strong yin energy starts to fade and yang energy begins to grow. Sufficient yang energy is crucial for people to stay active during the day, and it should be well-stored at the right time. Since sleep is the best way to store yang energy, it is best to be at deep sleep at zi, which means you should go to sleep at hai. People should not go outdoors from hai through zi.

To fall asleep, Dr Wang suggests lying on one side, with one bent leg lying on the other. One should also be calm and think of nothing. Only when the heart sleeps (thinks nothing) can deep sleep be enjoyed.

Hai is also considered the best time of the day for sex (also getting pregnant), when yin and yang are in balance in the body and in the universe, according to Qu Limin, author of the popular book "Twelve Hours and Health Maintenance." She says it's based on the daily schedule for health in the "Medical Classic of the Yellow Emperor," the foundational TCM text.

After spending time dining and talking with family and friends, one tends to be in a good mood, so it's time to feed the body with joy, says Qu. The Chinese character (pictograph) for hai itself pictures a man's arm cradling a woman's belly. The universe and the body area ready for new life.

Having sex at this time also leaves enough time for a sound sleep and rest for the next day.

According to TCM, one should avoid sex when the energy in the universe is disrupted (since it's also disrupted within the body): during heavy storms, high winds, other weather upheavals, earthquakes, eclipses of the sun and moon. Internal energy is disordered when one is drunk or has eaten too much, so in these cases it's best to wait to have sex.

In zi, you should be fast asleep.