The analysis of spring-like behavior of human body during unilateral and bilateral hopping tests with different strategies

Leg stiffness is one of the variables related to sports performance and lower extremity injuries. This variable is usually measured by hopping test. The aims of this study were to compare the leg stiffness between three strategies of hopping (maximal, preferred, controlled), and between three styles of hopping (bilateral, by dominant leg, by non-dominant leg) and the comparison of bilateral leg stiffness with the sum of the two leg stiffness.
27 Young healthy men performed hopping test on a force plate, in front of a high speed camera, in 9 methods (3 strategies × 3 styles). Leg stiffness was calculated by dividing the maximum vertical ground reaction force to vertical displacement of center of mass in contact phase. Repeated Measures ANOVA and Paired Sample T-Test were used to statistical analyses.
The main results of the study were non-significant difference in bilateral leg stiffness between 3 strategies, significant difference in dominant leg stiffness between preferred and controlled strategies, difference between dominant and non-dominant leg stiffness in maximal hopping, and violation of spring formula in amounts of unilateral and bilateral leg stiffness.
Based on the results, leg stiffness is dependent on the strategy and the style of hopping test and may not be in agreement with spring formulas and bilateral symmetry assumption. Considering these points may be important to determination of optimum leg stiffness to high athletic performance and low injury risk and diagnosis of the athletics at high risk of lower extremity injuries.