title: Upper limb muscle-bone asymmetries and bone adaptation in elite youth tennis players.
abstract: BACKGROUND
  The study of tennis players allows the nonracket arm to act as an internal control for the exercising racket arm. In addition, the study of the upper limbs removes the influence of gravitational loading, allowing the examination of the influence of muscular force on bone adaptation.
  
  
  METHODS
  The role of muscular action on bone, strength parameters of the radius, ulna (both at 4% and 60% distal-proximal ulnar length), and humerus (at 35% distal-proximal humerus length) as well as muscle size in both arms of 50 elite junior tennis players (mean ± SD age = 13.5 ± 1.9 yr) were measured with peripheral quantitative computed tomography (pQCT).
  
  
  RESULTS
  Strong relationships were found between muscle size and bone size in both arms (all correlations, P < 0.001, R = 0.73-0.86). However, the muscle-bone ratio was significantly lower (P < 0.001) in the upper arm on the racket side (compared with the contralateral arm). In addition, material eccentricity analysis revealed that bone strength in bending and torsion increased more than strength in compression as the moment arms for these actions (bone length and width, respectively) increased (in all cases, P > 0.001, R = 0.06-0.7) with relationships being stronger in torsion than in bending. Large side differences were found in bone strength parameters and muscle size in all investigated sites, with differences in distal radius total BMC (+37% ± 21%) and humerus cortical cross-sectional area (+40% ± 12%) being most pronounced (both P < 0.001).
  
  
  CONCLUSIONS
  These results support a strong influence of muscular action on bone adaptation; however, interarm muscle-bone asymmetries suggest factors other than local muscle size that determine bone strength. The results also suggest that torsional loads provide the greatest stress experienced by the bone during a tennis stroke.
authors.affiliation: Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, UK.
authors.forename: Alex
authors.initials: A
authors.lastname: Ireland
authors.forename: Thomas
authors.initials: T
authors.lastname: Maden-Wilkinson
authors.forename: Jamie
authors.initials: J
authors.lastname: McPhee
authors.forename: Karl
authors.initials: K
authors.lastname: Cooke
authors.forename: Marco
authors.initials: M
authors.lastname: Narici
authors.forename: Hans
authors.initials: H
authors.lastname: Degens
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D001132:Arm; D050280:Arm Bones / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D002648:Child; D005260:Female; D005542:Forearm; D007839:Functional Laterality; D006801:Humans; D006811:Humerus / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D008297:Male; D008572:Menarche / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D009929:Organ Size; D011884:Radius / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D013715:Tennis / Q000502:physiology*; D014057:Tomography, X-Ray Computed; D014457:Ulna / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology