title: Intensity of exercise is associated with bone density change in premenopausal women.
abstract: BACKGROUND
  High-impact exercise is known to be beneficial for bones. However, the optimal amount of exercise is not known. The aim of the present study was to evaluate the association between the intensity of exercise and bone mineral density (BMD).
  
  
  METHODS
  We performed a 12-month population-based trial with 120 women (aged 35-40 years) randomly assigned to an exercise group or to a control group. The intensity of the physical activity of 64 women was assessed with an accelerometer-based body movement monitor. The daily activity was analyzed at five acceleration levels (0.3-1.0 g, 1.1-2.4 g, 2.5-3.8 g, 3.9-5.3 g, and 5.4-9.2 g). BMD was measured at the hip, spine (L1-L4), and radius by dual-energy x-ray absorptiometry. The calcaneus was measured using quantitative ultrasound.
  
  
  RESULTS
  Physical activity that induced acceleration levels exceeding 3.9 g correlated positively with the BMD change in the hip area (p<0.05-0.001). L1 BMD change correlated positively with activity exceeding 5.4 g (p<0.05) and calcaneal speed of sound with the level of 1.1-2.4 g (p< 0.05). Baseline BMD was negatively associated with the BMD change at the hip.
  
  
  CONCLUSIONS
  The intensity of exercise, measured as the acceleration level of physical activity, was significantly correlated with BMD changes. Bone stimulation is reached during normal physical exercise in healthy premenopausal women. In the hip area, the threshold level for improving BMD is less than 100 accelerations per day at levels exceeding 3.9 g.
authors.affiliation: Department of Medical Technology, University of Oulu, P.O. Box 5000, 90014 Oulu, Finland. avainion@mail.student.oulu.fi
authors.forename: A
authors.initials: A
authors.lastname: Vainionpää
authors.forename: R
authors.initials: R
authors.lastname: Korpelainen
authors.forename: E
authors.initials: E
authors.lastname: Vihriälä
authors.forename: A
authors.initials: A
authors.lastname: Rinta-Paavola
authors.forename: J
authors.initials: J
authors.lastname: Leppäluoto
authors.forename: T
authors.initials: T
authors.lastname: Jämsä
mesh_terms: D000328:Adult; D000886:Anthropometry; D015519:Bone Density / Q000502:physiology*; D016022:Case-Control Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D005387:Finland; D006801:Humans; D010806:Physical Education and Training; D017697:Premenopause / Q000502:physiology*; D012044:Regression Analysis