title: Immediate effects of 2 different whole-body vibration frequencies on muscle peak torque and stiffness.
abstract: OBJECTIVE
  To examine the immediate effects of 2 vibration protocols with different vibration frequencies that yielded the same maximum acceleration (106.75ms(-2)) on muscle peak torque and stiffness of knee extensor and flexor.
  
  
  METHODS
  Randomized crossover study with repeated measures.
  
  
  METHODS
  Laboratory setting.
  
  
  METHODS
  Recreationally active male adults (N=10).
  
  
  METHODS
  Participants performed 10 bouts of 60-second static half squats intermitted with a 60-second rest period between bouts on a platform with no vibration (control) and a vibration frequency of 26Hz or 40Hz.
  
  
  METHODS
  Concentric and eccentric peak torques of knee extensor and flexor were examined within 5 minutes before and after vibration by isokinetic test. Young's modulus as an index of tissue stiffness was determined at quadriceps and hamstring pre- and postvibration by using an ultrasound indentation method.
  
  
  RESULTS
  The 2-way repeated-measures analysis of variance indicated a significant interaction effect between vibration and vibration frequency for knee extensor concentric peak torque (P=.003). The vibration-induced changes of knee extensor concentric peak torque in vibration frequency of 26Hz (14.5Nm) and 40Hz (12.0Nm) were found to be significantly greater than that in controls (-29.4Nm) (P<.05). The change in eccentric peak torque of knee flexor after vibration tended to be greater in 26Hz of vibration frequency when compared with controls (26Hz of vibration frequency vs controls: 13.9±7.1 vs -11.4±5.3Nm, P=.08). No statistically significant differences were obtained in tissue stiffness in the quadriceps and hamstring with any of the conditions.
  
  
  CONCLUSIONS
  Our data suggest that whole-body vibration at a frequency of 26Hz and 40Hz preclude the decline in concentric peak torque of knee extensor observed after 10 bouts of 60 seconds of static half squats. A change in muscle mechanical stiffness property as induced by whole-body vibration is not supported by our data.
authors.affiliation: Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, China. htpsiu@inet.polyu.edu.hk
authors.forename: Parco M
authors.initials: PM
authors.lastname: Siu
authors.forename: Bjorn T
authors.initials: BT
authors.lastname: Tam
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Chow
authors.forename: Jing-Yi
authors.initials: JY
authors.lastname: Guo
authors.forename: Yan-Ping
authors.initials: YP
authors.lastname: Huang
authors.forename: Yong-Ping
authors.initials: YP
authors.lastname: Zheng
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Wong
mesh_terms: D018592:Cross-Over Studies; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D026741:Physical Therapy Modalities; D016059:Range of Motion, Articular; D019415:Torque; D014732:Vibration / Q000627:therapeutic use*