title: Assessments of Mechanical Stiffness and Relationships to Performance Determinants in Middle-Distance Runners.
abstract: OBJECTIVE
  To examine relationships between methods of lower-limb stiffness and their associations with running economy (RE) and maximal velocity (vmax) in middle-distance (MD) runners.
  
  
  METHODS
  Eleven highly trained male MD runners performed a series of mechanical and physiological tests to determine maximal overground sprint speed, RE, and [Formula: see text]. Achilles tendon stiffness (kT) was estimated using ultrasonography during maximal isometric ankle plantar flexion. Global stiffness qualities were evaluated using a spring-mass model, providing measures of leg (kleg) and vertical stiffness (kvert) during running and jumping, respectively.
  
  
  RESULTS
  Very large (r = -.70) and large (r = -.60) negative relationships existed between RE and kTand kvert, during plantar flexion and unilateral jumps, respectively. There were large (r = .63) and extremely large (r = -.92) associations between kvertand kTand klegduring sprinting, respectively. Runners' vmaxhad large positive associations between kT(r = .52) and kleg(r = .59) during sprinting.
  
  
  CONCLUSIONS
  In well-trained MD athletes, greater stiffness appears linked to faster and more economical running. Although kThad the strongest relationship with RE, klegwhile sprinting and kvertin maximal unilateral jumps may be more practical measures of stiffness. Agreement between global stiffness assessments and kThighlights the energy contribution of the Achilles tendon to running efficiency and velocity. Further research incorporating these assessment tools could help establish more comprehensive mechanical and metabolic athlete profiles and further our understanding of training adaptations, especially stiffness modification, longitudinally.
authors.forename: Simon A
authors.initials: SA
authors.lastname: Rogers
authors.forename: Chris S
authors.initials: CS
authors.lastname: Whatman
authors.forename: Simon N
authors.initials: SN
authors.lastname: Pearson
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Kilding
mesh_terms: D000125:Achilles Tendon / Q000502:physiology*; D000293:Adolescent; D056352:Athletes; D054874:Athletic Performance / Q000502:physiology*; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D005082:Physical Exertion; D012420:Running / Q000502:physiology*; D055815:Young Adult
keywords: Achilles tendon; hopping; profiling; running economy; sprinting