[Study on the measurement of skinfold thickness and estimation of body composition in Chinese primary and secondary school students].

OBJECTIVE: To determine the patterns and characteristics of skinfold thickness and body composition of Chinese primary and secondary school students.

METHODS: 82,921 Han youths aged 7 through 18 were randomly selected from 13 provinces. Their biceps and subscapular skinfolds were measured and the body compositions were estimated by using Changling's and Brozek's models.

RESULTS: In boys, the biceps skinfolds reached the top of 10.9 mm, and then gradually decreased. The subscapular skinfolds increased rapidly from 5.7 mm in aged 7 to 8.7 mm in aged 12, and then slowly increased to 10.8 mm in aged 18. The biceps and subscapular skinfolds of girls gradually increased from 8.9 mm and 6.0 mm in aged 7, to 17.0 mm and 16.5 mm in aged 18, respectively. Their increments were especially large during the post-puberty period. The percentage of fat in boys increased from 14.0% in aged 7 to the relatively higher levels (16.1% - 17.6%) during aged 10 - 14, and then decreased significantly to about 13% in the 15 - 18 age groups. The percentage of fat in girls significantly increased from 19.6% in aged 7 to 23.0% in aged 12, and reached 25.6% in aged 18. The percentage of fat of the girls was significantly higher than that of the boys in all age groups. The lean body mass, both of the boys and girls, gradually increased from age 7 to age 18, but the absolute increments of boys were 12.1% higher in aged 7, 16.8% higher in aged 14, and 34% higher in aged 18 than that of girls, Significant differences of skinfold thickness were found not only among different areas and socioeconomic groups, but also between urban and rural populations. The percentile norms of the sum of skinfold thickness were set up, both for boys and girls, respectively. It was found that the P(50) of the norms were evidently lower than that of the Japanese, which showed the generally low level of Chinese students' skinfolds. But the differences of skinfolds between Chinese and Japanese in the high percentiles, such as the P(90), P(95) and P(97), were small, which suggested the subcutaneous body fat of many Chinese adolescents had already reached a quite high level.

CONCLUSIONS: It will be a big challenge to prevent obesity among Chinese students in the near future. The percentile norms set up in this study cover various age and sex groups of Chinese students. These norms will be useful for further screening obesity in Chinese students.