title: Lower extremity stiffness: implications for performance and injury.
abstract: BACKGROUND
  Lower extremity stiffness is thought to be an important factor in musculoskeletal performance. However, too little or too much stiffness is believed to increase the risk of musculoskeletal injury.
  
  
  OBJECTIVE
  To provide a current update of the lower extremity stiffness literature as it pertains to both performance and injury.
  
  
  CONCLUSIONS
  It appears that increased stiffness is beneficial to performance. As well it appears that there may be an optimal amount of stiffness that allows for injury-free performance. There is some evidence that increased stiffness may be related to bony injuries and decreased stiffness may be associated with soft tissue injuries. Further investigations should evaluate the relationship between stiffness and injury prospectively. Initial reports suggest that stiffness can be modified in response to the external environment or verbal cues.
  
  
  CONCLUSIONS
  A greater understanding of the role of stiffness in both performance and injury will provide a stronger foundation for the development of optimal training intervention programs.
authors.affiliation: Biomechanics and Movement Science Program, University of Delaware, Newark, DE 19716, USA. rbutler@udel.edu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Butler
authors.forename: Harrison P
authors.initials: HP
authors.lastname: Crowell
authors.forename: Irene McClay
authors.initials: IM
authors.lastname: Davis
mesh_terms: D004548:Elasticity; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D007866:Leg / Q000502:physiology*; D008022:Ligaments / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D017695:Soft Tissue Injuries / Q000503:physiopathology; D013710:Tendons / Q000502:physiology