title: Normative data and predictors of leg muscle function and postural control in children.
abstract: BACKGROUND
  At the present there are limited tools available to measure muscle function in young children. Ground reaction force plates measure lower-body function and postural control in older children and adults. The purpose of this study was threefold: 1) develop normative data for evaluating global muscle development; 2) determine the reproducibility of ground reaction force plates for assessing muscle function in preschool-age children; and 3) identify predictors of skeletal muscle function.
  
  
  METHODS
  Children's (n = 81, 1.8 to 6.0 yr; M = 52%) muscle function and postural control was measured for jump (JMP), sit-to-stand (STS), and both undistracted and distracted body sway tests using a ground reaction force plate (Kistler 9200A). Whole body composition used dual-energy x-ray absorptiometry (Hologic 4500A Discovery Series). Plasma 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone concentrations were measured by chemiluminescence (Liaison, Diasorin, Mississauga, ON, Canada) as well as ionized calcium (ABL80 FLEX, Radiometer Medical A/S). Demographics, and anthropometry were collected. ANOVA and linear regression were used to identify predictors. Reproducibility was assessed by intersubject coefficient of variation.
  
  
  RESULTS
  Age was a consistent predictor in all models; body size or fat and lean mass were important predictors in 3 of the models - STS peak force, STS peak power, and JMP peak power. STS was the most reproducible maneuver (average coefficient of variation =15.7%). Distracted body sway testing was not appropriate in these youngsters.
  
  
  CONCLUSIONS
  The novel data presented in this study demonstrate a clear age (developmental) effect without any effect of sex on muscle function and postural control in young children. Lean muscle mass was important in some models (STS peak force and JMP peak power). The STS test was the best of the 4 maneuvers.
authors.affiliation: 1Mary Emily Clinical Nutrition Research Unit, School of Dietetics and Human Nutrition, McGill University, Montreal, Quebec, CANADA; 2Department of Pediatrics, McGill University, Montreal, Quebec, CANADA; 3School of Physical and Occupational Therapy, McGill University, Montreal, Quebec, CANADA; and 4The Montreal Children's Hospital, Montreal, Quebec, CANADA.
authors.forename: Tom J
authors.initials: TJ
authors.lastname: Hazell
authors.forename: Atul K
authors.initials: AK
authors.lastname: Sharma
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Vanstone
authors.forename: Isabelle
authors.initials: I
authors.lastname: Gagnon
authors.forename: Thu Trang
authors.initials: TT
authors.lastname: Pham
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Finch
authors.forename: Hope A
authors.initials: HA
authors.lastname: Weiler
authors.forename: Celia J
authors.initials: CJ
authors.lastname: Rodd
mesh_terms: D000367:Age Factors; D015992:Body Mass Index; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007866:Leg / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010827:Physiology / Q000295:instrumentation; D011187:Posture / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D012737:Sex Factors