The Relation Of College Students' BMI To Body Composition And Some Physical Fitness Indicators

[Objectives]In 1990, WHO recommended body mass index (BMI) as a rough indicator of human obesity measurement, then BMI was widely used to measure human obesity and nutritional status. But BMI as a commonly used evaluating method neither accurately reflected the amount of body fat, nor showed the distribution of body fat. College students were a special group. A study found that compered with the day before 1990s, the current body composition of college students had been a marked change, becoming more body fat, but less fat free mass.And obesity was the result of excessive accumulation of body fat. Therefore, using body fat percentage (Fat%) as the gold standard, to explpre the physical results which determined by different BMI standards, and to explpre the relation of college students'BMI to body composition and some physical fitness indicators, provided a reference for related research.[Methods]295 subjects from Zhejiang University college students'volunteers were obtained in April 2010, of which 110 were male, female 185. According with the instructions of Biospace Body Composition Analyzer and "Students'Health Standards (trial)", the indicators were accessed as follows:total body fat(TBF), body fat percentage, fat free mass(FFM), skeletal muscle mass, protein, height, weight, waist circumference, hip circumference, chest circumference, circumference of upper arm relaxed, circumference of upper arm tense, vital capacity, grip strength, back strength. The following derived indicators were obtained in accordance with formula:BMI, waist-hip ratio, Weierweike index, upper arm circumference difference, vital capacity mass index, grip strength mass index, tensile index. The database was built with Excel and analyzed with SPSS16.0:Independent-Samples T Test, Kappa Test, One-Way ANOVA, Bivariate Correlate and Linear Regression were used.[Results]Using Fat% as the gold standard for diagnosis, compared with three criterias of BMI, the results suggested as follows. Male's sensitivity:Asia Pacific (72.7%)> Chinese obese group (63.6%)> WHO (54.5%); Male's kappa coefficient:WHO (0.598, P<0.001)> Chinese obese group (0.409, P<0.001)> Asia-Pacific region (0.311, P <0.001). Female's sensitivity:Asia Pacific (18.7%)> Chinese obese group (9.9%)> WHO (2.2%); Female's Kappa coefficient:Asia-Pacific region (0.168, P<0.001)> Chinese obese group (0.079, P= 0.026)> WHO (0.012, P=0.542).There was a moderate correlation between BMI and TBF (r=0.55, P<0.001). However, close correlation in both male and female (male:r=0.72, P<0.001; female: r=0.78, P<0.001) were fould. There was a moderate correlation between BMI and FFM (r=0.53, P<0.001), while stratified by gender, the correlation were different (male:r=0.67, P<0.001; female:r=0.42, P<0.001). The Linear regression analysis suggested that male's TBF and FFM had higher impact on BMI; while female's BMI was mainly affected by the amount of TBF.With the increasing of BMI, college students'vital capacity, grip strength, back strength gradually increased, however, the associated physical fitness mass indexs decreased. Correlation analysis suggested that BMI was positively correlated with vital capacity, grip strength, back strength, while BMI was negatively correlated with vital capacity mass index. Stratified by gender, male's BMI was negatively correlated with vital capacity mass index (r=-0.45, P<0.001), grip strength mass index (r=-0.38, P <0.001), tensile index (r=-0.21, P<0.001); and female's BMI was also negatively correlated with vital capacity mass index (r=-0.30, P<0.001), grip strength mass index (r=-0.38, P<0.001), tensile index (r=-0.31, P<0.001).[Conclusion]The current BMI standards affected female's evaluation results. Female's BMI cut-off points should be lower than male's. The increment of male's BMI was the effect of TBF and FFM increasing together. The level of BMI affected college students'physical fitness condition, and the influence degree should be evaluated in the form of physical fitness mass indexs.