title: Jump power and force have distinct associations with cortical bone parameters: findings from a population enriched by individuals with high bone mass.
abstract: BACKGROUND
  Little is known of the relationships between muscle function and bone, based on the recently developed technique of jumping mechanography.
  
  
  OBJECTIVE
  Our objective was to determine associations between peak ground reaction force and peak power during a 1-legged hopping test and a single 2-legged jump, respectively, and cortical bone parameters.
  
  
  METHODS
  This was a cross-sectional observational study in participants from the high bone mass cohort.
  
  
  METHODS
  Participants included 70 males (mean age 58 years) and 119 females (mean age 56 years); high bone mass cases and controls were pooled.
  
  
  METHODS
  Total hip bone mineral density (BMD) (measured by dual-energy x-ray absorptiometry scanning) and mid-tibial peripheral quantitative computed tomography (Stratec XCT2000L).
  
  
  RESULTS
  Jump power was positively related to hip BMD (standardized β [95% confidence interval]=0.29 [0.07, 0.51], P=.01), but hopping force was not (0.03 [-0.16, 0.22], P=.74) (linear regression analysis adjusted for age, gender, height, and weight). In 113 participants with force and peripheral quantitative computed tomography data, both jump power and hopping force were positively associated with tibial strength strain index (0.26 [0.09, 0.44], P<.01; and 0.24 [0.07, 0.42], P=.01 respectively). Although hopping force was positively associated with bone size (total bone area 0.22 [0.03, 0.42], P=.02), jump power was not (0.10 [-0.10, 0.30], P=.33). In contrast, jump power was inversely associated with endocortical circumference adjusted for periosteal circumference (-0.24 [-0.40, -0.08], P<.01) whereas no association was seen for hopping force (-0.10 [-0.26, 0.07], P=.24).
  
  
  CONCLUSIONS
  Although power and force are both positively associated with cortical bone strength, distinct mechanisms appear to be involved because power was primarily associated with reduced endocortical expansion (reflected by endocortical circumference adjusted for periosteal circumference, and hip BMD), whereas force was associated with increased periosteal expansion (reflected by total bone area).
authors.affiliation: Musculoskeletal Research Unit (S.A.H., C.L.G., J.H.T.), School of Clinical Sciences, University of Bristol, Bristol BS10 5NB, United Kingdom; Institute of Aerospace Medicine (J.R.), German Aerospace Center, D-51147 Cologne, Germany; Institute for Biomedical Research into Human Movement and Health Research Institute (J.R.), Manchester Metropolitan University, Manchester M1 5GD, United Kingdom; Birmingham Children's Hospital (N.C.), Birmingham B4 6NH, United Kingdom; and Nutrition and Bone Health, Medical Research Council Human Nutrition Research, Cambridge CB1 9NL, United Kingdom.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Hardcastle
authors.forename: Celia L
authors.initials: CL
authors.lastname: Gregson
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
authors.forename: Nicola
authors.initials: N
authors.lastname: Crabtree
authors.forename: Kate
authors.initials: K
authors.lastname: Ward
authors.forename: Jon H
authors.initials: JH
authors.lastname: Tobias
mesh_terms: D015519:Bone Density / Q000502:physiology*; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D006615:Hip / Q000000981:diagnostic imaging / Q000502:physiology; D006801:Humans; D007866:Leg; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D011859:Radiography; D013977:Tibia / Q000000981:diagnostic imaging / Q000502:physiology