Technical Note – Ballistic Measurement System – Defining Phases of the Countermovement Jump

PDF of this technical note is available here.

The Ballistic Measurement System Software Version 2021 can automatically locate the phases of a countermovement jump using criteria well established in the research literature (Krzyszkowski et al 2020). The three main phases are:

• eccentric
  1. start = time at which force drops 2.5% below body weight
  2. end = time of zero crossing of velocity from negative to positive
• concentric
  1. start = time of zero crossing of velocity from negative to positive
  2. end = time of takeoff defined as force dropping below threshold (default = 20N)
• flight
  1. start = time of takeoff defined as force dropping below threshold (default = 20N)
  2. end = time of landing defined as force rising above threshold (default = 20N)

Sub-Phases of the Eccentric Phase

The eccentric phase is further defined within the BMS software using the criteria of (Krzyszkowski et al 2020). These phases are:

• unloading
  1. start = time at which force drops 2.5% below body weight
  2. end = time of minimum force during eccentric phase
• yielding
  1. start = time of minimum force during eccentric phase
  2. end = time of peak negative COM velocity (i.e. time of lowest velocity)
• braking
  1. start= time of peak negative COM velocity (i.e. time of lowest velocity)
  2. end = time of zero crossing of velocity from negative to positive