Stiffness is an index for determination of elastic properties of body and its optimum range is different in various

motion patterns. The Spring-mass model is used for calculating stiffness. In this method, the whole leg is modeled

with a linear simple spring. The aim of this study is determination of lower body stiffness and evaluation of its

correlation with agility, as dominant motion pattern in racket sports. 12 national-level male racket-players (age:

25±4 years & weight: 80±7 kg) participated voluntarily in this study. Leg and vertical stiffness were measured

during running on treadmill and hopping test. Pearson’s correlation coefficients were used to examine the

relationships between stiffness and agility test records. Statistical significance was set at P< 0.05. There wasn’t

significant correlation with agility in this study. The reason could be of the contrast influence of knee and ankle

stiffness on performance. This problem requires separate evaluation of joint stiffness.