title: Modulation of bone's sensitivity to low-intensity vibrations by acceleration magnitude, vibration duration, and number of bouts.
abstract: Variables defining vibration-based biomechanical treatments were tested by their ability to affect the musculoskeleton in the growing mouse. Duration of a vibration bout, but not variations in vibration intensity or number of vibration bouts per day, was identified as modulator of trabecular bone formation rates.
  
  
  BACKGROUND
  Low-intensity vibrations (LIV) may enhance musculoskeletal properties, but little is known regarding the role that individual LIV variables play. We determined whether acceleration magnitude and/or the number and duration of daily loading bouts may modulate LIV efficacy.
  
  
  METHODS
  LIV was applied to 8-week-old mice at either 0.3 g or 0.6 g for three weeks; the number of daily bouts was one, two, or four, and the duration of a single bout was 15, 30, or 60 min. A frequency of 45 Hz was used throughout.
  
  
  RESULTS
  LIV induced tibial cortical surface strains in 4-month-old mice of approximately 10 με at 0.3 g and 30 με at 0.6 g. In trabecular bone of the proximal tibial metaphysis, all single daily bout signal combinations with the exception of a single 15 min daily bout at 0.3 g (i.e., single bouts of 30 and 60 min at 0.3 g and 15 and 30 min at 0.6 g) produced greater bone formation rates (BFR/BS) than in controls. Across all signal combinations, 30 and 60 min bouts were significantly more effective than 15 min bouts in raising BFR/BS above control levels. Increasing the number of daily bouts or partitioning a single daily bout into several shorter bouts did not potentiate efficacy and in some instances led to BFR/BS that was not significantly different from those in controls. Bone chemical and muscle properties were similar across all groups.
  
  
  CONCLUSIONS
  These data may provide a basis towards optimization of LIV efficacy and indicate that in the growing mouse skeleton, increasing bout duration from 15 to 30 or 60 min positively influences BFR/BS.
authors.affiliation: Department of Biomedical Engineering, Stony Brook University, Bioengineering Building, Rm 213, Stony Brook, NY, 11794-5281, USA, stefan.judex@stonybrook.edu.
authors.forename: S
authors.initials: S
authors.lastname: Judex
authors.forename: T J
authors.initials: TJ
authors.lastname: Koh
authors.forename: L
authors.initials: L
authors.lastname: Xie
mesh_terms: D000818:Animals; D001835:Body Weight / Q000502:physiology; D001862:Bone Resorption / Q000503:physiopathology; D008297:Male; D008807:Mice, Inbred BALB C; D018482:Muscle, Skeletal / Q000033:anatomy & histology; D010012:Osteogenesis / Q000502:physiology*; D013314:Stress, Mechanical; D013977:Tibia / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D013997:Time Factors; D014732:Vibration; D055114:X-Ray Microtomography / Q000379:methods