How Vertical Stiffness, Depth Jumps and Eccentric Demands are Tied Together
In the picture above, the landing on the left is from a smaller box while the landing on the right is from a lager box.
An increase in box height increased the landing velocity and eccentric forces.
As you can see, with a taller box the athlete is unable to maintain vertical stiffness and “gives” into the forces. This only occurs when the eccentric force becomes too great and the eccentric demands are not converted and stored as elastic energy. Instead, this creates two distinct phases of movement (braking then propulsion).
This was highlighted by a reduction in jump height and RSI from the taller box compared to the smaller box.
Note, this athlete is plenty strong (squats 2x bw and about 3x on the trap bar deadlift). However, compared to a similar body weight athlete with less strength, the stronger athlete failed to match the weaker athlete’s RSI and jump height from the taller box.
Strength can be built in the weight room with traditional exercises, but adding specific movements to target vertical stiffness are necessary.
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