Objective: A better understanding of the role of muscle fatigue in lower limb stiffness during performance will provide a strong foundation for the development of optimal training intervention programs. This study aimed to investigate the effect of fatigue on ankle and knee joints and leg stiffness during a 30-scontinuous vertical jump test.
Methods: Fifteen female volleyball players without history of lower extremity injuries were selected in this study. They performed a 30 seconds vertical jump test and kinetics and kinematics data were measured using a force plate and two video cameras, respectively. Lower limb, stiffness before and after fatigue (first 10 percent of the jump, 10% percent of the end jump) were compared using a paired samples t-test analysis. The amount of relationship between the height of the jump and leg, ankle and knee joints stiffness were measured by the use of Pearson test (P <0/05 ).
Results: Results showed a significant reduction in knee and ankle joints stiffness (pknee= 0.00, pankle= 0.004) and leg stiffness (p=0.01) during the test. In other words, fatigue decreases leg stiffness and ankle and knee joints stiffness by 20%, 47% and 34%, respectively. It also decreases the jump height and ground reaction force.
Conclusion: As the height of the jump and stiffness changes in lower body parts is an important factor in fields such as volleyball, coaches need to pay due attention to stiffness changes and improve their training techniques.