Investigation of the Relationship between Lower Extremity Stiffness and Selected Biomechanical Variables Associated with the Risk of Injury in Healthy Physically Active Young Male Adults

Stiffness is one of the characteristic of viscoelastic structures in human body that can theoretically affect the risk of injury. The objective of this study was to determine the relationship between the lower limb stiffness and selected biomechanical variables related to the risk of injury in healthy physically active young male adults.

20 male physical education students participated voluntarily in this study. They performed vertical hopping tests in three styles, bilateral, unilateral on dominant leg and unilateral on non-dominant leg, with three strategies, preferred and control (frequency 2.2 Hz) and the maximal to determine the stiffness of the lower limb and performed one-leg landing to determine the peak of vertical ground reaction force, rate of loading and mechanical absorbed energy. The variables were estimated by the force plate and the motion analysis system. The relationship between lower limb stiffness and selected biomechanical variables (peak of vertical ground reaction force, rate of loading and mechanical absorbed energy) in landing was determined by Pearson correlation test (p ≤ 0.05).

Among the lower limb stiffness variables during hopping performance with different strategies (control strategy, preferential and maximal), lower limb stiffness during maximal unilateral hopping tests showed significant and positive relationship with peak of vertical ground reaction force (p = 0.01) and rate of loading (p = 0.01). Lower limb stiffness during control hopping tests showed a significant negative relationship with the mechanical absorbed energy (p = 0.02).

According to the findings, it can be argued that the high lower limb stiffness increases the risk of bony injuries such as knee osteoarthritis and stress fractures, while low lower limb stiffness increases the risk of soft tissue injuries. Therefore, it seems that very low or very high lower limb stiffness is not an advantage in order to reduce the risk of injury, and there is probably some optimal value for it.