When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this, you make the time of the impact about 10 times as great as for a stiff-legged landing. In this way the average force your body experiences is

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The force experienced by the body during impact is inversely proportional to the time over which the impact occurs. By increasing the time of impact (by bending the knees), the average force experienced is reduced. According to the impulse-momentum theorem, $F \Delta t = \Delta p$, where $F$ is the average force, $\Delta t$ is the time over which the force acts, and $\Delta p$ is the change in momentum. Increasing $\Delta t$ decreases $F$, making it about 1/10 as great for a 10 times increase in impact time.

When You Jump from an Elevated Position You Usually Bend