[Reference values of skeletal muscle mass for children in Nanjing area].

Objective: To establish the reference values and growth curves of skeletal muscle mass among children in the Nanjing area. Methods: A cross-sectional study was conducted with children who underwent physical examination at the Department of Child Health Care, Children's Hospital of Nanjing Medical University from 2020 January to 2022 September. Their height, weight, body fat mass and skeletal muscle mass were measured. Body mass index, percentage of body fat mass, percentage of skeletal muscle mass, relative skeletal muscle mass index and the ratio of skeletal muscle to body fat were calculated. The associations between skeletal muscle mass indices and physical measurements index were analyzed through the Spearman correlation test. The Mann-Kendall test was used to assess the trend for skeletal muscle mass. Generalized additive models for location, scale and shape were used to construct percentile reference values and growth curves of male and female skeletal muscle mass indices at different ages. Results: A total of 32 690 children aged 4-14 years were enrolled in this study, including 19 912 boys (60.91%). Skeletal muscle mass, percentage of skeletal muscle mass, relative skeletal muscle mass index and the ratio of skeletal muscle to body fat of boys and girls was 11.10 (8.40, 14.90) and 10.30 (7.90, 13.20) kg, 40.36% (37.01%, 43.13%) and 39.38% (36.43%, 41.88%), 6.70 (6.07, 7.52) and 6.33 (5.79, 7.00), 2.39 (1.46, 3.47) and 2.14 (1.45, 3.00) kg/m2, respectively. Skeletal muscle mass of both boys and girls was all positively associated with weight (r=0.97, 0.96), body mass index (r=0.68, 0.63) and percentage of body fat mass (r=0.40, 0.43) (all P<0.01). The reference values and growth curves showed that the percentage of skeletal muscle mass P50 ranged from 37.75%-44.61% in boys and from 36.22%-40.55% in girls. The relative skeletal muscle mass index P50 ranged from 5.80-9.68 kg/m2 in boys and from 5.57-7.98 kg/m2 in girls. The ratio of skeletal muscle to body fat P50 ranged from 1.86-2.67 in boys and from 1.29-2.41 in girls. There was an increasing trend with age for both boys and girls in the growth of skeletal muscle mass (Z=4.20, 3.75, both Ptrend<0.01), and increased slightly before 9 years of age and then increased rapidly until 14 years of age in both boys and girls. Conclusions: The skeletal muscle mass indices change with age and gender during childhood. Percentile reference values for pediatric skeletal muscle mass indices can be used to evaluate the muscular growth and development in children in the Nanjing area.目的： 建立南京地区儿童骨骼肌质量及其相关指标的参照值及骨骼肌质量生长曲线，为临床评估儿童骨骼肌生长水平提供参考标准。 方法： 横断面研究，以2020年1月至2022年9月在南京医科大学附属儿童医院儿童保健科健康体检的32 690名4~14岁儿童为研究对象，测量儿童身高、体重，应用生物电阻抗法测定体脂质量、骨骼肌质量，计算体质指数、体脂百分比、骨骼肌质量百分比、相对骨骼肌质量指数和肌脂比。采用Spearman相关分析方法分析骨骼肌质量相关指标与体格测量指标之间的相关性，趋势性检验使用Mann-Kendall检验。采用基于位置、尺度和形状的广义可加模型方法按照性别、年龄构建骨骼肌质量及其相关指标百分位参照值及骨骼肌质量生长曲线。 结果： 32 690名儿童中男19 912名（60.91%），男、女童骨骼肌质量、骨骼肌质量百分比、相对骨骼肌质量指数、肌脂比分别为11.10（8.40，14.90）和10.30（7.90，13.20）kg、40.36%（37.01%，43.13%）和39.38%（36.43%，41.88%）、6.70（6.07，7.52）和6.33（5.79，7.00）kg/m2、2.39（1.46，3.47）和2.14（1.45，3.00）。男、女童骨骼肌质量与体重（r=0.97、0.96），体质指数（r=0.68、0.63），体脂百分比（r=0.40、0.43）均正相关（均P<0.01）。骨骼肌质量及指数的百分位参照值和骨骼肌质量生长曲线图显示，男、女童骨骼肌质量百分比在P50上分别波动在37.75%~44.61%和36.22%~40.55%，相对骨骼肌质量指数在P50上分别波动在5.80~9.68 kg/m2和5.57~7.98 kg/m2，肌脂比在P50上分别波动在1.86~2.67和1.29~2.41；男、女童骨骼肌质量均随年龄的增加而增加（Z=4.20、3.75，均P趋势<0.01），9岁前增长缓慢，9岁后增长加快。 结论： 儿童骨骼肌的生长发育存在年龄、性别差异。建立南京地区4~14岁男女童骨骼肌质量及其相关指标百分位参照值，补充了儿童体格生长和营养状况评价系统。.