title: Changes in speed skating velocity in relation to push-off effectiveness.
abstract: Speed skating posture, or technique, is characterized by the push-off angle or effectiveness (e), determined as the angle between the push-off leg and the ice; the preextension knee angle (θ(0)); and the trunk angle (θ(1)). Together with muscle-power output and environmental conditions, skating posture, or technique, determines velocity (v).
  
  
  OBJECTIVE
  To gain insight into technical variables that are important to skate efficiently and perform well, e, θ(0), θ(1), and skating v were determined every lap during a 5000-m World Cup. Second, the authors evaluated if changes (Δ) in e, θ(0), and θ(1) are associated with Δv.
  
  
  METHODS
  One camera filmed the skaters from a frontal view, from which e was determined. Another camera filmed the skaters from a sagittal view, from which θ(0) and θ(1) were determined. Radio-frequency identification tags around the ankles of the skaters measured v.
  
  
  RESULTS
  During the race, e progressively increased and v progressively decreased, while θ(0) and θ(1) showed a less consistent pattern of change. Generalized estimating equations showed that Δe is significantly associated with Δv over the midsection of the race (β = -0.10, P < .001) and that Δθ(0) and Δθ(1) are not significantly associated with Δv.
  
  
  CONCLUSIONS
  The decrease in skating v over the race is not due to increases in power losses to air friction, as knee and trunk angle were not significantly associated with changes in velocity. The decrease in velocity can be partly ascribed to the decrease in effectiveness, which reflects a decrease in power production associated with fatigue.
authors: MOVE Research Institute Amsterdam, the Faculty of Human Movement Sciences, VU University Amsterdam, The Netherlands.
authors: Dionne A
authors: DA
authors: Noordhof
authors: Carl
authors: C
authors: Foster
authors: Marco J M
authors: MJ
authors: Hoozemans
authors: Jos J
authors: JJ
authors: de Koning
mesh_terms: D000054:Acceleration; D000704:Analysis of Variance; D054874:Athletic Performance / Q000502:physiology*; D001696:Biomechanical Phenomena; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D011187:Posture / Q000502:physiology; D012861:Skating / Q000502:physiology; D014741:Video Recording