What is the difference between RSI and mRSI?

RSI stands for Reactive Strength Index.

  • RSI is the ratio of Flight Time & Ground Contact Time
  • RSI = Flight Time / Ground Contact Time
  • Time To Take-Off (TTT) can be substituted for Ground Contact Time if the movement being performed is a Countermovement Jump.
  • There is no unit for RSI.

mRSI stands for Modified Reactive Strength Index.

  • mRSI is the ratio of Jump Height & Ground Contact Time
  • mRSI = Jump Height / Ground Contact Time
  • Time To Take-Off (TTT) can be substituted for Ground Contact Time if the movement being performed is a Countermovement Jump.
  • There is no unit for mRSI.

Practical Application

  • RSI and mRSI are typically used as a way to measure an athlete's reactive strength ability. These metrics helps answer the questions...
    • How elastic is this athlete?
    • How effectively do they use their stretch-shortening cycle?
    • Do we need to work on this quality?
  • Assessments of reactive strength include...
    • Fast Explosive Strength: drop jump, countermovement rebound jump, and multi rebound jump.
    • Slow Explosive Strength: countermovement jump
  • What is a good mRSI value?
    • This figure below shows RSI on the righthand sign, however Eamonn is using the equation Jump Height / Contact Time. These values are best used when analyzing mRSI during a drop jump off of a 30cm box.
      This figure above is an except from the Train With Push blog post titled 'THE REACTIVE STRENGTH INDEX REVISITED - PART 2 BY EAMONN FLANAGAN'
  • Learn more about Reactive Strength Assessment in our blog here.
  • Want to learn more about how to program for athlete's based off of their Reactive Strength values? Take advantage of our Sport Science Consulting Packages. Email us at info@hawkindynamics.com to learn more.