EFFECTS OF FLEXIBILITY EXERCISES TO PREVENT KNEE INJURIES IN TENNIS PLAYERS

ABSTRACT Introduction: Despite the intrinsic benefits of sports practice, the adherence to tennis by a large part of the population without the due physical preparation apparently resulted in a high rate of knee joint injuries in tennis players, either in daily training or competitions. Objective: Prevent tennis players’ knee joint injuries by exploring ways to improve lower limb joint stability. Methods: This paper selected 50 national second-level professional tennis players and divided them into two groups. Both groups had daily tennis training, but the experimental group experienced additional lower limb flexibility exercises. Results: The tennis players in the experimental group increased their seated forward flexion from 22.19 cm to 26.96 cm, the knee joint extensor muscle strength index increased from 142.69 to 176.23, and the knee joint flexor muscle strength index increased from 93.21 to 149.28, P<0.05, with significant differences. The general stability index was changed from 0.23 to 0.20, the internal and external indices varied from 0.13 to 0.08, and the frontal and posterior indices changed from 0.13 to 0.08. Conclusion: Knee joint injuries in tennis players can be effectively combated by adding lower limb flexibility exercise protocol to daily training. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.


INTRODUCTION
As a famous ball game in the world, tennis started relatively late in China compared with other ball games.Like other ball games, tennis is also an explosive sport, which has high requirements for the flexibility of tennis players' lower limbs. 1 At present, due to the late start of China's tennis, China's tennis does not have great advantages in international competitions.At the same time, in many professional tennis competitions in the world, the performance of Chinese tennis players is not very good. 2 There is a big gap between the physical quality and tennis skills of Chinese tennis players and the world's top tennis players.With the continuous promotion of China's sports power strategy, we should constantly improve the physical quality and tennis skills of Chinese tennis players.In order to cultivate more high-quality tennis players and promote the development of tennis in China. 3In tennis, not only the joint movement of tennis players is required, but also the physical flexibility of tennis players is required.When tennis players serve and receive the ball, the strength of serving, the speed of running on the court and the endurance of hitting the ball will be affected by the flexibility of the lower limbs. 4If tennis players have good flexibility of lower limbs, they will have higher endurance and strength when playing tennis.The flexibility of the lower limbs is crucial to the improvement of the professional level of tennis players. 5At the same time, tennis players with high flexibility of lower limbs will also have less sports injury of knee joint.As the most complex joint in human body structure, knee joint has very powerful functions.At the same time, the bearing capacity of the knee joint is very strong. 6Make every effort.Even without muscle support, the knee joint can well bear the weight of the body alone.In tennis.The force on the knee joint is relatively large.Any slight change can easily cause injury to the knee joint. 7Therefore, it is very important to explore the lower limb flexibility of tennis players to prevent sports injuries.

METHOD Research object
In order to avoid the difference in physical fitness due to gender differences, this paper selected 50 professional young male tennis players as the research object, and conducted a 14-week experiment at the tennis training center.The study and all the participants were reviewed and approved by Ethics Committee of Shanghai University of Finance and Economics Zhejiang College (NO.SHUFE20F015).The specific situation of 50 professional male tennis players selected in this study is shown in Table 1.The age of 50 male tennis players is between 22 and 23 years old, the average height is 175 cm, the average weight is 72 kg, the exercise duration is more than 6 years, and the exercise level is the national second level.50 professional young male tennis players were randomly divided into two groups, with 25 tennis players in each group.

Research methods
50 professional male tennis players were divided into two groups, one of which was the experimental group.The other group was the control group.The experimental group was trained in lower limb flexibility.Before and after tennis, the sports stretching is carried out by combining the dynamic and static characteristics.Select professional coaches and experts to guide tennis players' flexibility training to prevent sports injuries.The training includes transverse fork, left longitudinal fork, right longitudinal fork and forward bending in sitting position.The control group did not receive any lower limb flexibility training, but only received normal tennis training.Before and after training, the age, height and.Record the basic physical fitness information.At the same time, the flexibility information of tennis players should be recorded.

Control of experimental factors
The only independent variable in this experiment is the method and action of stretching.The dependent variable is the lower limb flexibility test index of tennis players.In the course of this study, the research objectives, the strength of flexibility movement and the density of flexibility movement are all guided by professional coaches.During this experiment.The control group only received tennis training.In addition to daily tennis training, the experimental group also needs to carry out lower limb flexibility training.In addition, neither group did any training.

Changes of flexibility quality of tennis players after lower limb flexibility training
From Table 2, it can be seen that the tennis players in the control group increased their sitting forward bending from 22.382cm before the experiment to 25.245cm after the experiment, and the degree of vertical leg splitting of the left and right legs changed from 169.336 ° and 170.953 ° before the experiment to 173.843 ° and 171.555 ° after the experiment, with a small change.The extensor muscle strength of the knee joint increased from 147.575 before the experiment to 188.607 after the experiment.The flexor muscle strength of the knee joint increased from 85.953 before the experiment to 130.234 after the experiment.
It can be seen from Table 3 that the tennis players in the experimental group increased their sitting forward bending from 22.193cm before the experiment to 26.964cm after the experiment, p<0.01, with a very significant difference.The degree of vertical split of the left and right legs changed from 169.245 ° and 170.861 ° before the experiment to 178.856 ° and 177.153 ° after the experiment.There was a significant difference between the degree of vertical split of the left leg and the degree of vertical split of the right leg (p<0.05), and there was a very significant difference between the degree of vertical split of the right Due to the significant difference between P<0.05 and P<0.01, it can be found from the comparative experiment results that the tennis players in the control group have no significant changes in the flexibility indicators of the lower limbs without any flexibility training, P values are greater than 0.05, and there is no significant difference.Under the guidance of the coach, the experimental group carried out regular flexibility.Before and after the experiment, the various flexibility indicators of its lower limbs had significant changes, P values were less than 0.05, there was a significant difference.In particular, the changes of body flexion in sitting position are the most obvious, with very significant differences.This shows that lower limb flexibility training can effectively improve the flexibility quality of tennis players, and then make tennis players better play in the field and achieve better results.

Prevention effect of lower limb flexibility exercise on tennis players' knee joint injury
Table 4 shows that the overall stability index of tennis players in the control group was 0.259 before the experiment and 0.244 after the experiment, p>0.05, with no significant difference.The internal and external index was 0.142 before the experiment and 0.119 after the experiment, p<0.05, with significant difference.The anteroposterior index was 0.132 before the experiment and 0.120 after the experiment, p<0.05, with significant difference.The comprehensive score of Y balance test was 97.195 before the experiment and 108.646 after the experiment (p<0.05), with significant difference.
Table 5 shows that the overall stability index of tennis players in the experimental group was 0.239 before the experiment and 0.203 after the experiment, p>0.05, with no significant difference.The internal and external index was 0.132 before the experiment and 0.081 after the experiment, p<0.05, with significant difference.The anteroposterior index was 0.132 before the experiment and 0.084 after the experiment, p<0.05, with significant difference.The comprehensive score of Y balance test was 94.489 before the experiment and 108.757 after the experiment (p<0.05), with significant difference.
Before and after the experiment, the range of knee stability of tennis players in the control group who did not have lower limb flexibility exercise was lower than that in the experimental group.At the same time, the indexes of knee stability of tennis players in the control group after the experiment were also lower than that in the experimental group.This shows that the lower limb flexibility exercise can significantly improve the knee stability of tennis players, and there are significant changes in the overall stability index, the lateral and lateral index, the anteroposterior index, and the comprehensive score of Y balance test.However, there is no significant difference in the overall stability index between the experimental group and the control group, indicating that the improvement of the overall stability index is difficult, or the effect is not obvious in the short term.In the future professional tennis training, we can increase the flexibility of athletes and prevent sports injuries by increasing the flexibility of lower limbs.

DISCUSSION
The knee joint is the most important joint of the lower limb of the human body.Whether it is in the slow movement or in the rapid antagonistic movement, the knee joint bears various contradictory forces.Especially in tennis, because tennis includes many sports within the limits of physical fitness.There are injuries caused by various sports in the process of tennis.At the same time, because of the strong antagonism of tennis.If unscientific and unreasonable tennis training methods are adopted in the daily tennis training, and there is no professional coach to guide, it is likely to cause knee injury.Tennis coaches not only need to master the most basic tennis training knowledge, but also need to know some anatomy related knowledge, so as to better guide athletes in training and prevent knee injury.The knee joint plays a role in adjusting muscles and ligaments in tennis.However, if the knee joint is injured in the daily tennis training and tennis competition, the knee joint cannot perform these functions normally, and cannot play its functions normally, which will cause greater damage.
The physical quality of tennis players is very important, and it is the key factor to improve the skill level of tennis players.The improvement of tennis players' physical quality can not only improve tennis players' competition endurance, but also help to more effectively prevent physical injuries caused by sports, and is conducive to tennis players' physical health.So how to test the sports level and training results of tennis players?Tennis competition is a very important way.Through tennis competition, the skill level of tennis players can be effectively tested.At the same time, tennis competition can also attract public attention and attention, and stimulate public enthusiasm for tennis competition.But.The frequent holding of tennis matches also means higher requirements for the physical quality of tennis players.In the process of frequent preparation for tennis matches, tennis players need to constantly improve their physical quality and improve their flexibility.Every tennis match is an explosion of strength.Once the movement is unreasonable and exceeds the physical limit, it is easy to cause injury to tennis players.The research results of this paper show that the lower limb flexibility exercise can effectively improve the lower limb flexibility of tennis players, provide a good buffer for the explosive force impact of tennis players, and effectively prevent the knee joint injury for tennis players.

CONCLUSION
In recent years, with the development of tennis in China, the upsurge of tennis has gradually arisen in China.There is a deep research on the training content and methods of tennis in China.However, there are still deficiencies in the flexibility of the lower limbs of tennis.Knee joint, as a very important organ of human lower limb, is easy to cause injury to tennis players in their daily training.In recent years, people pay more attention to the prevention of knee joint injury.In daily tennis training, if high intensity training is carried out frequently, it is easy to cause injury to the knee joint.Once an athlete makes a mistake, it will cause greater injury to the knee joint and affect the performance of the athlete.At the same time, because tennis is not a mild sport, its sports intensity is

Table 1 .
Basic information of the tennis players studied.

Table 2 .
Changes in the flexibility quality of tennis players in the control group.

Table 3 .
Changes of flexibility quality of tennis players in the experimental group.The extensor muscle strength of the knee joint increased from 142.693 before the experiment to 176.236 after the experiment (p<0.01), with a very significant difference.The flexor muscle strength of knee joint increased from 93.210 before the experiment to 149.285 after the experiment (p<0.05), with significant difference.

Table 4 .
Changes of knee joint stability of tennis players in the control group.

Table 5 .
Changes of knee joint stability of tennis players in the experimental group.