title: Weekly training hours are associated with molecular and cellular body composition levels in adolescent athletes.
abstract: OBJECTIVE
  We aimed to explore associations between hours per week of sports training and molecular and cellular body composition components in adolescent athletes.
  
  
  METHODS
  A total of 33 female athletes (13.3+/-3.5 years; 47.8+/-12.6 kg; 154+/-14.0 cm) and 90 male athletes (14.1+/-2.7 years; 60.6+/-17.8 kg; 167+/-16.2 cm) were measured. Based on the total of hours per week of training, athletes were divided into tertiles: <4.5 h/week; 4.5-8.9 h/week; 9 h/week. Dual-energy X-ray absorptiometry (DXA) was used to assess lean mass (lean), body fat (BF), percent body fat (%BF), bone mineral content (BMC) and density (BMD). Total body water (TBW), intracellular (ICW) and extracellular water (ECW) were assessed using bioelectrical impedance spectroscopy (BIS). Extracellular fluids (ECF), solids (ECS), body cell mass (BCM) and body fluid distribution (E/I) were calculated. Total hours per week of sports training (h/week), habitual physical activity (PA) and dietary were assessed by questionnaire. Statistics included analysis of covariance (ANCOVA) and simple regression analyses.
  
  
  RESULTS
  Athletes training 9 h/week presented greater levels of TBW, lean, bone mass, BCM, and ECF and a lower %BF, independently of confounders. No significant differences in body composition estimates were found between athletes training <9 h/week. Hours per week of sports training were positively associated with fat free components, only in the group exercising 9 h/week
  
  
  CONCLUSIONS
  In this group of Portuguese athletes from different sports we observed that training 9 h/week significantly improved body composition, especially fat free components, which may be important for a healthy growth and sports performance.
authors.affiliation: Exercise and Health Laboratory, Faculty of Human Movement, Technical University of Lisbon, Cruz Quebrada, Lisbon, Portugal.
authors.forename: A L
authors.initials: AL
authors.lastname: Quiterio
authors.forename: E A
authors.initials: EA
authors.lastname: Carnero
authors.forename: A M
authors.initials: AM
authors.lastname: Silva
authors.forename: F
authors.initials: F
authors.lastname: Baptista
authors.forename: L B
authors.initials: LB
authors.lastname: Sardinha
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D054874:Athletic Performance / Q000502:physiology*; D001823:Body Composition / Q000502:physiology*; D001834:Body Water / Q000502:physiology*; D015519:Bone Density / Q000502:physiology*; D003430:Cross-Sectional Studies; D017097:Electric Impedance; D015444:Exercise / Q000502:physiology*; D045604:Extracellular Fluid / Q000378:metabolism*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D013177:Sports / Q000502:physiology*; D011795:Surveys and Questionnaires; D013997:Time Factors