title: Muscle function, dynamic loading, and femoral neck structure in pediatric females.
abstract: OBJECTIVE
  Muscle forces influence the development of bone mass and structure, but dynamic loading via impact exercise is considered particularly osteogenic. We hypothesized that indices of local muscle function and physical activity exposure would predict femoral neck (FN) structure in premenarcheal females.
  
  
  METHODS
  We tested this hypothesis in 76 healthy, premenarcheal girls (46 gymnasts and 30 nongymnasts). Height, weight, Tanner breast stage, and prior year nonaquatic, organized physical activity level (PAL) were recorded semiannually. Hologic dual-energy x-ray absorptiometry scans (whole body, left FN) yielded total body nonbone lean mass and bone outcomes, including narrow neck (NN) hip structural analysis data. Dynamometers assessed nondominant hand grip and left hip flexion/extension indices. Parsimonious regression models tested the following as predictors of bone outcomes: local muscle function, PAL, gymnast status, and lean mass, accounting for Tanner breast stage and height, as appropriate.
  
  
  RESULTS
  Hip flexion indices were significantly correlated with indices of FN mass, density, structure, and strength (P < 0.05). However, the entry of PAL, gymnast status, and lean mass into regression models supplanted local muscle function explanatory value. In contrast, for many variables, the significant association of gymnast status persisted after accounting for physical maturity, body size/lean mass, and PAL. For all skeletal indices except FNArea, NNwidth, NN endosteal diameter, and NN buckling ratio, gymnast status was more strongly associated with bone outcomes than PAL.
  
  
  CONCLUSIONS
  Greater activity doses and exposure to extreme dynamic loading provide independent benefits to FN structure during growth. Furthermore, weight-bearing activity and high-impact exercise exposure appear superior to local muscle force measures for prediction of FN structure.
authors.affiliation: 1Department of Orthopedic Surgery, SUNY Upstate Medical University, Syracuse, NY; 2Department of Exercise Science, Syracuse University, Syracuse, NY; 3Department of Public Health and Preventive Medicine, SUNY Upstate Medical University, Syracuse, NY; 4Vitality Program, College of Health Professions, SUNY Upstate Medical University, Syracuse, NY; and 5Department of Orthopedics and Rehabilitation, University of Wisconsin, Madison, WI.
authors.forename: Jodi N
authors.initials: JN
authors.lastname: Dowthwaite
authors.forename: Paula F
authors.initials: PF
authors.lastname: Rosenbaum
authors.forename: Carol A
authors.initials: CA
authors.lastname: Sames
authors.forename: Tamara A
authors.initials: TA
authors.lastname: Scerpella
mesh_terms: D000293:Adolescent; D015992:Body Mass Index; D002648:Child; D005260:Female; D005272:Femur Neck / Q000033:anatomy & histology* / Q000502:physiology; D006173:Gymnastics / Q000502:physiology; D006801:Humans; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D010012:Osteogenesis; D011627:Puberty; D055070:Resistance Training; D016474:Weight-Bearing
references.citation: J Bone Miner Res. 1999 Jul;14(7):1222-30
references.pmid: 10404025
references.citation: Osteoporos Int. 2011 Jul;22(7):2205-10
references.pmid: 20838772
references.citation: J Bone Miner Res. 2005 May;20(5):809-16
references.pmid: 15824854
references.citation: J Bone Miner Res. 1998 Mar;13(3):500-7
references.pmid: 9525351
references.citation: J Bone Miner Res. 1992 Nov;7(11):1291-6
references.pmid: 1466254
references.citation: J Clin Densitom. 2013 Jan-Mar;16(1):92-7
references.pmid: 22980488
references.citation: Sports Med. 2003;33(10):727-43
references.pmid: 12895130
references.citation: J Musculoskelet Neuronal Interact. 2010 Mar;10(1):3-11
references.pmid: 20190375
references.citation: Bone. 2011 May 1;48(5):1103-8
references.pmid: 21241839
references.citation: Med Sci Sports Exerc. 2008 Jun;40(6):1135-41
references.pmid: 18460991
references.citation: Bone. 2004 May;34(5):771-5
references.pmid: 15121007
references.citation: J Bone Joint Surg Am. 1984 Mar;66(3):397-402
references.pmid: 6699056
references.citation: J Musculoskelet Neuronal Interact. 2009 Jan-Mar;9(1):2-14
references.pmid: 19240362
references.citation: J Bone Miner Res. 2002 Jun;17(6):1095-101
references.pmid: 12054165
references.citation: J Bone Miner Res. 2005 Mar;20(3):520-8
references.pmid: 15746998
references.citation: Bone. 2006 Jun;38(6):871-7
references.pmid: 16431171
references.citation: Osteoporos Int. 2011 Jan;22(1):207-16
references.pmid: 20419293
references.citation: J Bone Miner Res. 2001 Feb;16(2):195-201
references.pmid: 11204418
references.citation: Bone. 2005 Jun;36(6):1030-8
references.pmid: 15878316
references.citation: J Musculoskelet Neuronal Interact. 2005 Jul-Sep;5(3):232-8
references.pmid: 16172514
references.citation: Bone. 2012 May;50(5):1173-83
references.pmid: 22342799
references.citation: J Appl Physiol (1985). 2010 Jun;108(6):1737-44
references.pmid: 20378706
references.citation: J Bone Miner Res. 2012 Jan;27(1):104-10
references.pmid: 21956460
references.citation: Bone. 2003 Sep;33(3):317-29
references.pmid: 13678772
references.citation: Med Sci Sports Exerc. 2009 Nov;41(11):2044-9
references.pmid: 19812512
references.citation: J Bone Miner Res. 2002 Mar;17(3):363-72
references.pmid: 11874228
references.citation: J Bone Miner Res. 1992 Jul;7(7):761-9
references.pmid: 1642145
references.citation: J Sports Med Phys Fitness. 2004 Mar;44(1):98-103
references.pmid: 15181397
references.citation: Eur J Pediatr. 2010 Mar;169(3):281-7
references.pmid: 19526369
references.citation: J Bone Miner Res. 2009 Dec;24(12):1981-8
references.pmid: 19453258
references.citation: J Anat. 2009 Feb;214(2):197-207
references.pmid: 19207981
references.citation: Bone. 2007 May;40(5):1196-202
references.pmid: 17258519
references.citation: J Bone Miner Res. 2008 Jul;23(7):1002-11
references.pmid: 18302501
references.citation: Pediatr Exerc Sci. 2010 Feb;22(1):21-33
references.pmid: 20332537
references.citation: Bone. 2005 Jul;37(1):112-21
references.pmid: 15869917
references.citation: J Musculoskelet Neuronal Interact. 2012 Jun;12(2):56-67
references.pmid: 22647278