ANALYZING VERTICAL JUMP GROUND REACTION FORCES USING YANK-TIME ASSESSMENTS – PROPOSING AN ALTERNATIVE ASSESSMENT METHOD
Andrew C. Fry1, Matthew Hermes1
1University of Kansas, Lawrence, KS
Studies analyzing vertical ground reaction forces (GRF) have determined there are characteristic patterns related to vertical jumping (VJ) ability (Guess et al. 2020, Sanfilippo et al. 2016). It was recently suggested that a more detailed analysis is possible using the instantaneous 1st derivative of force (N×s-1) expressed across time, called yank, to examine unique characteristics of the force-time curve for a VJ (Sahrom et al. 2020). Analysis of yank permits determining key points and phases in the VJ GRF curve, such as when the slopes of the curves change directionally or are increasing or decreasing. Shown below are examples of four unique shapes of VJ GRF curves (n=1 each), several of which have been identified by principle components analysis (Guess et al. 2020, Sanfilippo et al. 2016). The yank-events (solid lines) are as follows; 1 – start of the countermovement, 2 – bottom of the first yank trough (slope of rate of decreasing force starts decreasing), 3 – increasing yank crosses 0 (lowest force), 4 – decreasing yank crosses 0 (1st force peak), 5 – increasing yank crosses 0 (separates 2 force peaks when present), 6 – decreasing yank crosses 0 (2nd force peak when present), 7 – take-off (GRF = 0, just past lowest yank). The dotted lines indicate the traditionally defined VJ “braking phase”. Previous reports suggest VJ variation 2 in particular, and possibly 3, are conducive to higher VJ, which are both accompanied by generally increasing yank values in the braking phase. Also, peak velocity for VJ variation 1, which is associated with low VJ heights, occurs when yank is below 0, unlike all other VJ variations (see arrows). Finally, durations of each phase can be determined, both normative and absolute, to help evaluate and understand different VJ mechanics and responses to training and exercise.
Fry, AC and Hermes, M
"ANALYZING VERTICAL JUMP GROUND REACTION FORCES USING YANK-TIME ASSESSMENTS – PROPOSING AN ALTERNATIVE ASSESSMENT METHOD,"
International Journal of Exercise Science: Conference Proceedings: Vol. 11:
9, Article 21.
Available at: https://digitalcommons.wku.edu/ijesab/vol11/iss9/21