Extended Abstract
1. Introduction
roper lower limb function is one of the most essential factors of participating in sports activities [1, 2]. Most of the ligament injuries have occurred during landings and rotations, as the most important mechanisms in the occurrence of lower limb injuries [3]. Functional stability is one of the essential indicators for participating in sports [3], and plays an important role in people's activities, including simple daily tasks and high-level performances in sports based on their nature [4]. In this regard, proprioception as a very effective part of somatosensory system, plays a significant role in maintaining the balance of people. Therefore, any weakness and impairment in proprioception significantly increases the risk of injuries to athletes [5]. 
Since proprioception sense is responsible for collecting information for the central nervous system to be informed of different parts of the body in relation to each other, any factor that disrupts this sense is a cause of damage and must be controlled. One of the factors that impair the proprioception sense is fatigue, because it increases the threshold of muscle spindle discharge, disrupting afferent feedback, and causing change in the joint awareness [6]. Studies have shown that in the onset of fatigue, neuromuscular control is impaired and due to delayed neuromuscular activation, shear forces and torque increase which impair joint stability [7, 8]. Many sports that require cognitive activity are prone to mental fatigue; however, lower limb injuries in these sports are high. Due to the considerable effect of mental fatigue on the occurrence of injury and the fact that no research has been done in this field so far, this study aimed to evaluate the effect of yoga training on knee proprioception and balance after mental fatigue in amateur athletes.
2. Methods
In this quasi-experimental study with pretest/posttest design using control group, the study population consisted of all male physical education students of Razi University in Kermanshah, Iran during the second semester. Of these, 36 were selected as study samples and were divided into two groups of training (n=18) and control (n=18) randomly using Random Number Allocation software. The training group performed yoga for 8 weeks, while control group received no intervention. Study outcomes included: dynamic balance (Y-test), semi-dynamic balance (Lafayette Stability Platform) and knee joint proprioception (reconstruction error at 30 and 60 degrees angles). Each subject was assessed in three stages: before the intervention, after the fatigue protocol, and eight weeks after receiving the mental fatigue protocol (follow-up). To compare the mean values, repeated measures ANOVA (two groups in three times) was used. All statistical analyzes were performed in SPSS v. 22 software.
3. Results
For active and passive knee proprioception as well as static and dynamic balances, repeated measures ANOVA results showed that the effect of time (P=0.001) and time-group interaction (P=0.001) was significant. Moreover, the results of Benfroni post hoc test showed that these changes between pretest and posttest phases and between posttest and follow-up phases were statistically significant (P=0.001). 
4. Discussion
The results of this study showed that yoga training inhibit mental fatigue by increasing the adaptive capacity of neurocognitive systems and modulating the autonomic nervous system, and can improve the balance function and knee joint proprioception by creating physical stability. It is possible that yoga helps to increase adaptation by reducing stress, and brings peace of body and mind to humans by limiting tension and reducing arousal in the cerebral cortex [9]. Some sports scientists have considered the fatigue issue as one of the negative factors affecting athletic performance and its relationship with postural control, because fatigue and impaired postural control can be causes of musculoskeletal injuries in athletes [10]. 
Martino et al. reported that after mental fatigue, due to the accumulation of adenosine in the brain, increased resistance to effort, feeling and perception of fatigue and lack of energy were observed [11]. Some other researchers have reported a quantitative and qualitative decrease in the technical performance of footballers due to mental and physical fatigue. Kastem et al. reported that endurance performance (time to reach fatigue, ability to speed up activity) decreased as a result of mental fatigue [12]. The results of these studies are consistent with our findings.
5. Conclusion
Yoga exercise can significantly improve balance and knee joint proprioception in amateur athletes. Mental fatigue is caused by long-term cognitive activities; it can affect balance control and perception of joint position and movement, and reducing the performance of athletes by exposing them to lower limb injuries. Therefore, doing yoga exercises to control and raise the threshold of mental fatigue can be a suitable intervention.
Ethical Considerations
Compliance with ethical guidelines
All ethical principles are considered in this article. This study was approved by the Ethics Committee of  Razi University (Code: IR.RAZI.REC.1398.001). 
Funding
The present paper was extracted from the MSc. thesis of the first author, Department of Corrective Exercises and Sport Injuries, Faculty of Physical Education, Razi University.
Authors' contributions
All authors contributed in preparing this article.
Conflicts of interest
The authors declared no conflict of interest.
Acknowledgements
Thus, authors thanks and appreciation the Razi University Physical Education Administration and the physical education students who participated in the test.