MOST people want their children to grow tall, especially in China where many parents believe summer is prime time for bone growth and use all kinds of ways to give their kids a leg up. Zhang Qian reports.

Right after finishing his vacation homework, 9-year-old Benny has a new task - jumping to reach the ball suspended from a door frame, at least 30 times a day.

Benny's height of 127cm, a little short for his age, didn't concern his parents until some of his shorter classmates shot up in height and surpassed him this year.

Now Benny's father says it's necessary to use summer vacation to help him catch up through exercise and special nutrition, known as reinforcing therapy in traditional Chinese medicine. There's a common belief in China that children's bones grow faster in summer.

"Jumping and reaching for the ball will help stretch the body vertically, which will help him grow taller," his father says. "That's what my father taught me when I was young; it worked for me and I believe it will work for Benny, too."

A healthy body and above average height is every parent's wish. The general advantages of height are documented in studies worldwide. Taller people were probably more successful in evolutionary terms in competition for resources.

Today there's a positive correlation between height and wages, even political office. Tall men also tend to attract more desirable mates.

In China, height is traditionally an important aesthetic criterion for a man's good looks (comparable to large eyes for women) and ability to attract a suitable wife. It's generally accepted that 180cm is an ideal height, especially in the eyes of the bride's parents, while those below 170cm may be teased as "second-rate" or "disabled." Women at 165cm are generally considered more desirable than shorter women.

"I wouldn't expect my son-in-law as handsome as a movie star, but at least he should be tall and have a good physique, making him look like a man who can protect," says 53-year-old Qiao Anmei, who has a 24-year-old unmarried daughter.

If a child is unusually short for his or her age, parents worry he or she will be disadvantaged later in life. Short children also tend to be bullied more than larger children.

So obsessed are some people with height that adults have been known to undergo grueling and expensive leg-lengthening procedures that involve cutting bones and attaching devices to create space and induce bone growth. These procedures can take as long as a year and the patient is wheel-chair bound for many months.

Height is determined by genetics and other factors such as diet, environment and exercise.

It's estimated that genetics accounts for around 70 percent of a person's height, leaving around 30 percent that can be influenced. Many parents are eager to help their children grow as tall as possible and they make use of summertime when, according to TCM, the universe is dominated by yang ("hot") energy. Yang is associated with growth, expansion, upward and outward movement and masculine energy.

They have come up various ways, basically involving stretching and nutrition.

Much of one's height is determined by the long bones in the legs and since physical stress stimulates growth of bone tissues, exercise is an important way to promote growth.

The focus on height is especially evident with boys.

Benny's routine of jumping and reaching is one of the popular approaches, while other parents require their children to do various other exercises to stretch their legs and spinal columns. Standing on tiptoes and reaching high above the head is one way; another is pull-ups or simply hanging from a horizontal bar.

Helpless stretching

Stretching can help some children grow taller, while it doesn't have much impact on others.

Daisy Xu, now 25 years old and 154cm, a little short, remembers that when she was a teenager she lay in bed and grabbed the sides of the bed while her mother pulled her legs - every night. She thinks her mother considered her too weak to do pull-ups.

"I know it sounds ridiculous, but we both believed that it would work and we persisted until I was 18 and there was little improvement," Xu says. "It was a hopeless plan of helpless people."

Chinese place great importance on diet and what's called food-reinforcement therapy to adjust one's energy balance and influence the system, including children's growth. Calcium-rich milk, which is known to promote healthy bones, is a must, as it is everywhere. In addition, energy-reinforcing foods such as pigeon, soft-shelled turtle and beef are popular ingredients in growth recipes, commonly soup.

In traditional medicine there's a theory that eating bones is good for bones, heart for the heart, liver for the liver, and so on. So some mothers make soup out of lots of bones that are boiled a long time.

Shirley Lin, 34, recently replaced rice in her son's diet with noodles, buns and pancakes made of wheat flour. She says an auntie once told her that people in northern China, generally taller than those in the south, overwhelmingly prefer wheat to rice. And she thinks wheat may help her son grow tall.

Some parents even resort to injections of human growth hormone (HGH) and medicines that are supposed to boost children's growth. Most experts are strongly opposed to using HGH for healthy children solely for cosmetic purposes of height.

It is used in cases of hormone deficiency and abnormal shortness. It's also used by some bodybuilders and athletes. Some doctors are willing to prescribe medication since it boosts their income.

"It is true that genetics account for much of a person's height, but there are still things we can do in the natural way," says David Chen, president of the Shanghai Height Improvement Research Center attached to the Shanghai Air Naval Hospital. "Sufficient outdoor exercise, good sleep and balanced nutrition can help children grow better, as long their bone age is still under 18 years," Chen says.

Sufficient and balanced nutrition (good protein, fat, carbohydrates, fiber, vitamins and minerals) doesn't necessarily mean a heavy "reinforcing" diet, he says. For example, more milk than necessary won't make bones grow longer. High-calorie diets of junk food, sweets and fried food are not healthy and lack required nutrition.

If parents are concerned about a child's height, Dr Chen suggests tests to determine any nutritional deficiency and adjusting the diet accordingly.

Exercise and games

He recommends physical exercise like basketball, badminton, running and jumping games, not necessarily the stretching exercises that many parents demand. The passive stretching in the case of Daisy Xu, whose mother pulled her legs, may be useless, Dr Chen says.

Vigorous activity is important because it promotes bone growth, secretion of growth hormone and calcium metabolism in bones. Outdoor exercise is preferable because it lets the body produce vitamin D from ultraviolet rays.

Regardless the amount of schoolwork, Dr Chen recommends at least half an hour to an hour of physical activity every day.

Growth hormone is naturally secreted in deep sleep, so plenty of sleep is necessary for good growth. Dr Chen says that generally children 3 to 6 years old need 10 to 12 hours of sleep a day, middle school students need nine to 10 hours and high school students need eight to nine hours.