Methods / Statistics

Document Type



The present study analyzed ground reaction forces that occur during a counter-movement vertical jump (CMVJ) to examine how measures assessing stretch-shortening cycle (SSC) interact. The participants consisted of thirteen recreationally active males that volunteered for this study. Vertical ground reaction forces were measured using a force platform sampling at 1000 Hz and exported into an RStudio vertical jump program for further analysis. A simple linear regression was performed to investigate the relationship between vertical stiffness and modified reactive strength index (RSImod). Modified reactive strength index was a significant predictor of vertical stiffness (p = .010, Adj. R2= .421). These results suggest that further examination of the mathematical equation used for RSImod is needed to eliminate possible effects of confounding variables as relationship differences were observed with the vertical stiffness measure that has been used for adequate assessment of the lower extremity muscle-tendon units’ status during counter-movement vertical jumping and other movements utilizing the SSC.