The effect of surface stiffness on the biomechanical behavior of the lower limb

The stiffness of sports surface, as one of the effective factors on traveling forces between human and surface, could affect the frequency and severity of sports injuries. However, there is little information regarding the effect of area elastic surface stiffness on the movement mechanics and applied forces. So, the purpose of this study was to identify the effect of surface stiffness on biomechanical behavior of lower limb.
In order to calculate leg stiffness, knee and ankle joint stiffness and vertical ground reaction force of 15 young male with the age range of 18-33 and weight range of 60-88 kg during hopping on the five different surfaces ranging from 200 to 500 kN/m, we used motion analysis and force platform systems.
results of ANOVA and Bonferroni Post-hoc test showed significant differences in the leg stiffness between 200 kN/m surface and force plate (P=0.04), between 300 kN/m and force plate (P=0.03) and between 400 kN/m and force plate (P=0.007); in the maximum ground reaction force between 200 kN/m surface and force plate (P=0.01) and between 200 and 500 kN/m surface (P=0.003) and finally in the ankle stiffness between 300 and 400 kN/m surface (P=0.04).
The results of this study showed that unlike common opinion that increase in surface stiffness causes the decrease in leg stiffness and vice versa, the interaction between surface stiffness and leg stiffness is only limited to surfaces with lower range of stiffness that resemble the leg stiffness value. Furthermore, if the limb stiffness increases, the suggested hypothesis fails to be accepted.