The effects of muscle mass and muscle quality on cardio-metabolic risk in peripubertal girls: a longitudinal study from childhood to early adulthood

BACKGROUND: Increased cardio-metabolic risk is well documented in children and adolescents with obesity and normal weight obesity (NWO). However, the associations of muscle mass and muscle quality with cardio-metabolic risk, independent of weight status from childhood to adulthood, has not been examined. METHODS: A total of 236 girls were followed from pre-puberty to early adulthood. Fat mass (FM) and lean mass (LM) of the whole body were assessed by a dual-energy X-ray absorptiometry; muscle cross-sectional area (mCSA), muscle density (mDen; skeletal muscle fat content) of the lower leg by the peripheral quantitative computerized tomography; and blood glucose, insulin, triglycerides and high-density lipoprotein cholesterol by enzymatic photometric methods. Study participants were categorized based on body mass index (BMI) and percentage body fat (%BF) as overweight and/or obese (BMI >= 30 with %BF >= 30), normal weight obese (BMI 18.5-24.9 with %BF >= 30) and normal weight lean (BMI 18.5-24.9 with %BF <30). RESULTS: Girls with overweight and/or obesity from age of 11 to age 18 had greater LM and larger mCSA, but lower mDen and skeletal muscle mass index than the normal-weight girls (P < 0.001 for all). Girls with NWO had similar mCSA and muscle mass but lower mDen and skeletal muscle index (SMI) than their normal-weight lean peers from childhood to early adulthood (P < 0.001 all). In all girls, mDen and SMI were inversely associated with cardio-metabolic risk score (r(2) = 0.012, P < 0.05 and r(2) = 0.201, P < 0.001, respectively). However, after adjusting for whole-body FM or android abdominal FM, all associations disappeared. CONCLUSIONS: Skeletal muscle size and muscle mass are not associated with cardio-metabolic risk factors during pubertal growth after adjusting for measures of adiposity. Ectopic fat accumulation in the skeletal muscle and increased adiposity, particularly in the abdominal area in childhood, are significant contributors to increased cardio-metabolic risk in adulthood, irrespective of body weight status.