title: A new sledge jump system that allows almost natural reactive jumps.
abstract: OBJECTIVE
  Sledge jump systems (SJS) are often employed to examine the underlying mechanical and neuromuscular mechanisms of the stretch-shortening cycle (SSC) as they allow the systematic variation of impact velocity and energy. However, in existing SJS the jumps are not very comparable to natural jumps because of the long contact times (∼200%), which prevent the storage of kinetic energy. The aim of the present study was to evaluate if an ultra-light sledge, built in a way that joint movement is barely restricted, allows jumps that are comparable to natural jumps.
  
  
  METHODS
  Ground reaction forces, kinematic and electromyographic (EMG) data of 21 healthy subjects were compared between normal hoppings (NH) on the ground and hoppings in a custom-built SJS (sledge hoppings, SH).
  
  
  RESULTS
  Normalized to NH, the ground contact times for the SH were prolonged (+22%), while the peak forces (-21%) and the preactivity of the soleus and gastrocnemius medialis muscles were reduced (-20% and -22%, respectively). No significant changes were observed for the iEMG of the short latency response of those muscles (+1% and +8%) and the ranges of motion in the ankle, knee and hip joint (differences of 1, 1 and 2 degrees). The reduced peak forces were associated with a reduced leg stiffness (-21%).
  
  
  CONCLUSIONS
  The new system allows reactive jumps that are rather comparable to natural jumps. Therefore, the new SJS seems to be an adequate system in order to examine the SSC under controlled and almost natural conditions.
authors.affiliation: Department of Sport and Sport Science, University of Freiburg, Germany. andreas_kramer@web.de
authors.forename: A
authors.initials: A
authors.lastname: Kramer
authors.forename: R
authors.initials: R
authors.lastname: Ritzmann
authors.forename: A
authors.initials: A
authors.lastname: Gollhofer
authors.forename: D
authors.initials: D
authors.lastname: Gehring
authors.forename: M
authors.initials: M
authors.lastname: Gruber
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D004576:Electromyography; D015444:Exercise / Q000502:physiology; D005260:Female; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology; D055815:Young Adult