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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.

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Objective: The number of people suffering from Osteoarthritis (OA) is increasing. Treatment of OA can be done with or without surgery. The most common treatment is using orthosis. However, most patients with OA prefer not to use orthosis because of downward transition. Therefore, the objective of this study was to design new orthosis and to assess its effects on knee joint kinetics and kinematics during gait.
Methods: Ten subjects without any neuromuscular disease participated in this study. New orhosis with the same structure of Scottish rite orthosis was designed. Qualysis system analyses with seven cameras as well as a Kistler force plate were used to measure the kinematics and kinetics variables during the gait with and without orthosis. For statistical analysis independent student-t test was used. The significance level was set at p<0.05.
Results: Mean walking speed with and without orthosis was not significantly different (p=0.42). Peak anterior- posterior forces applied on knee in the first half of stance phase and propulsion phase was the same during walking with and without orthosis (p>0.05). There was significant difference between peak medio-lateral forces applied on knee during walking with and without orthosis (p<0.05). Conclusion: The new orthosis decreases the adductor moment on knee joint therefore, it can decrease the forces applied on medial compartment of the knee joint. This orthosis improves walking because it does not let inferior transition. This orthosis can improve femur alignment. It is recommended that physiotherapist prescribe this orthosis in order to decrease pain in patients with OA.

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Objective: The purpose of this study is to find the optimum training conditions for selective strengthening of the vastus medialis oblique muscle over vastus lateralis.

Methods: For this purpose, a musculoskeletal model of lower limb was developed by OpenSim software. Using a detailed tibiofemoral and patellofemoral joint modeling and six muscular branches for components of quadriceps femoris muscle on the other hand, training conditions were simulated in isometric, isokinetic and isotonic modes. For each training condition, the motion kinematic and external force was applied to the model. After analyzing the inverse dynamics, the force of each component of quadriceps femoris muscle was obtained through the statical optimization. Impact of knee angle, speed of movement, external loading level and axial tibial rotation on activity rate of vastus medialis oblique to vastus lateralis muscle was investigated based on the model.

Results: The results showed that the knee angle affect on this ratio and the highest ratio could be obtained in angles close to full extension of knee. Speed of movement and external load level would not affect the ratio. Meanwhile axial tibial rotation could affect this ratio in a way that increasing tibial external rotation was associated with increasing the ratio.

Conclusion: The results indicate that high-speed isokinetic training with highest levels of tibial external rotation in angles close to full extension of knee can resulte in increasing the maximum activity ratio of vastus medialis oblique to vastus lateralis muscle.

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 Objective: The aim of this study was to test the effect of proprioception exercises in the rehabilitation process of football players after arthroscopic surgery on anterior cruciate ligament (ACL).
Method: Data was collected from Specialist Hospital and Research Center in Rehabilitation, Medicine and Sports, Moscow, Russia. 20 patients with an average age of 16-25 years old with no historical records of neuromuscular diseases and injuries of the lower extremities. These were randomly divided into two groups: one experimental and one control. The experimental group were under monitoring for about five months, while they were doing proprioceptive exercises. Before and after the training period, the static equilibrium from the stork test and the dynamic performance of the star test were estimated and compared. Data were analyzed using Mann-Whitney and t-test with the significance threshold of (p<0.05).
Results: through the proprioceptive exercise protocol, static and dynamic balance was significantly improved (p<0.001).
Conclusion: This study confirmed that proprioception exercises classified from simple to complex according to sport fields in different phases of rehabilitation can positively affect the balance, the performance and quick return of football players to sports fields.

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Objective Excessive dynamic knee valgus, as a defective movement pattern, predisposes patients to lower limb injuries. Therefore, the aim of the present study was to study dynamic knee valgus in male soccer players.
Methods In this review article, an attempt was made to collect studies conducted on the subject of research from 2000 to June 2021. The websites Google Scholar, PubMed, Science Direct, SID, ISC and Magiran were used and keywords related to the topic were used to search for articles.  
Results According to the search method, 50 articles were found, which were finalized according to the inclusion and exclusion criteria of 12 articles. Finally, 7 articles were reported in the present study. Dynamic knee valgus condition is more common in women than men, and varus are more common with increasing age of male soccer players. Different situations during the game such as tackling, jumping, imbalance after strike to the ball and landing after jumping are also among the situations that are associated with increased dynamic knee valgus and players are exposed to knee injury. The first minutes of the halves due to the lower angle of flexion of the knee and also late in the game due to fatigue can increase the dynamic valgus and increase the risk of knee injury. 
Conclusion All studies have pointed to the role of dynamic valgus in the incidence of knee joint injuries, especially the anterior cruciate ligament, so it is necessary to identify the mechanism of injury and correct the direction of dynamic valgus among soccer players.