title: Application of force-length curve for determination of leg stiffness during a vertical jump.
abstract: OBJECTIVE
  The aim of this study was to present the methodology for estimation of a leg stiffness during a countermovement jump. The question was asked whether leg stiffness in the countermovement and take-off phases are similar to each other as demonstrated in previous reports. It was also examined whether the stiffness in left lower limb is similar to the one in right lower limb.
  
  
  METHODS
  The research was conducted on 35 basketball players. Each participant performed three countermovement jumps with arm swing to the maximum height. Measurements employed a Kistlerforce plate and a BTS SMART system for motion analysis. Leg stiffness (understood as an inclination of the curve of ground reaction forces vs. length) was computed for these parts of countermovement and take-off phases where its value was relatively constant and F(Δl) relationship was similar to linear.
  
  
  RESULTS
  Mean value (±SD) of total stiffness of both lower limbs in the countermovement phase was 7.1 ± 2.3 kN/m, whereas this value in the take-off phase was 7.5 ± 1 kN/m. No statistically significant differences were found between the leg stiffness in the countermovement and the take-off phases. No statistically significant differences were found during the comparison of the stiffness in the right and left lower limb.
  
  
  CONCLUSIONS
  The calculation methodology allows us to estimate the value of leg stiffness based on the actual shape of F(Δl) curve rather than on extreme values of ΔF and Δl. Despite different tasks of the countermovement and the take-off phases, leg stiffness in these phases is very similar. Leg stiffness during a single vertical jump maintains a relatively constant value in the parts with a small value of acceleration.
authors.affiliation: Department of Team Sport Games, University School of Physical Education, Wrocław, Poland.
authors.forename: Artur
authors.initials: A
authors.lastname: Struzik
authors.affiliation: Department of Biomechanics, University School of Physical Education, Wrocław, Poland.
authors.forename: Jerzy
authors.initials: J
authors.lastname: Zawadzki
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D007866:Leg / Q000502:physiology*; D008954:Models, Biological; D009043:Motor Activity / Q000502:physiology*; D009068:Movement; D055815:Young Adult