title: [The differences in bone mineral content between female dancers and controls aged 15 - 17 years old and its relationship with physical activity level].
abstract: OBJECTIVE
  To assess bone mineral content (BMC) of 15 - 17 year-old dancers and high school females and analyze the relationship between physical activity status and BMC.
  
  
  METHODS
  Sixty dancers and 77 healthy controls aged 15 - 17 years old were enrolled in our study. BMC in the total body and forearm were measured by dual-energy X-ray absorptiometry (DEXA) while body weight and height were also measured. Physical activity information was collected by "one-year physical activity questionnaire".
  
  
  RESULTS
  The physical activity level (PAL) and the average daily energy expenditure (EE) of dancers were all higher than controls (PAL: 2.17 +/- 0.34 vs 1.63 +/- 0.34, t = 7.283; EE: (6876.43 +/- 1036.72) kJ vs (5388.43 +/- 920.83) kJ, t = 7.214, both P values < 0.01). The dancers showed lower BMC/height at total body and arms compared with the controls (the total body BMC/height was (13.896 +/- 1.308) vs (14.494 +/- 1.272) g/cm, F = -2.563); and the BMC/height of left and right arm were (0.779 +/- 0.088) vs (0.829 +/- 0.101) g/cm (F = -2.892) and (0.766 +/- 0.093) vs (0.829 +/- 0.097) g/cm (F = -3.650) respectively, all these P values were < 0.01.Yet after adjusting age and BMI, the dancers showed higher BMC/height at total body and legs, the corresponding values were (14.550 +/- 0.146) vs (13.947 +/- 0.131) g/cm (F = 7.868), (2.681 +/- 0.033) vs (2.389 +/- 0.030) g/cm (F = 36.520), (2.821 +/- 0.031) vs (2.450 +/- 0.028) g/cm (F = 65.279), all these P values were < 0.01. While no differences were found with controls at non-weight bearing sites (arms). Daily period (h) of training was significantly related to BMC/height of legs, total body (r value were 0.618, 0.448 and 0.554 respectively, all the P values < 0.01), while the history of training was also correlated with BMC/height of two legs (r value were 0.38 and 0.304 respectively, both P values < 0.05).
  
  
  CONCLUSIONS
  The adolescent dancers showed higher BMC after adjusting age and BMI, which was attributed to the long-term high level weight-bearing physical activity.
authors.affiliation: National Institute for Nutrition and Food Safety, Chinese Center for Disease Control and Prevention, Beijing 100050, China. lichen_yang@yahoo.com.cn
authors.forename: Li-chen
authors.initials: LC
authors.lastname: Yang
authors.forename: Jing
authors.initials: J
authors.lastname: Hu
authors.forename: Yan
authors.initials: Y
authors.lastname: Lan
authors.forename: Yan-hua
authors.initials: YH
authors.lastname: Yang
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhang
authors.forename: Jian-hua
authors.initials: JH
authors.lastname: Piao
mesh_terms: D000293:Adolescent; D015992:Body Mass Index; D015519:Bone Density; D003615:Dancing; D005260:Female; D006801:Humans; D009043:Motor Activity; D013334:Students