According to Table 2.1 and Figure 2.1, among the table-tennis undergraduates in colleges and universities in Liaoning Province investigated in this study, the occurrence times of sports injuries were 274 times in total. The occurrence time of sports injury only involves "in practice" and "after practice". The "pre-practice" period has not yet been covered. Among them, the occurrence time of sports injury in "practice" accounted for the largest proportion, accounting for nearly 95 percent, statistical times of 260, accounting for 94.89 percent.

Figure 2.1 percentage of time distribution of the time of sports injury

The proportion of "after practice" was only about 5 percent, and the number of statistics was only 14 times, which accounted for only 5.11 percent. On the whole, the occurrence time of sports injury is mainly in the undergraduate group of table tennis specialized in colleges and universities in Liaoning Province investigated by this research Focus on the practice. This is because in the process of learning and practicing table tennis skills and tactics, may be due to their own physical skills, skills and tactics are not firm. And equipment or emergency and other factors may lead to the occurrence of sports injuries.

Figure 2.3: the percentage distribution of people with different degrees of sports injury

According to Table 2.5 and Figure 2.3, among the table-tennis undergraduates in colleges and universities in Liaoning Province investigated by this research, the number of sports injuries was 341 times. "Mild" (normal practice), "moderate" (adjusted practice), "severe" (suspension) are involved in varying degrees. Among them, the degree of sports injury as "mild" accounted for the largest proportion, Accounted for far more than half of the total,    with    208    statistical    times,    accounting    for   61.00 %.The proportion of "moderate" in the degree of sports injury is the second largest, accounting for more than one-third, with 126 statistical times, accounting for 36.95 %. At the end of the list was "severe" in the nature of sports injuries, which accounted for the smallest proportion, with only 7 statistics, accounting for only 2.05 %.On the whole, among the undergraduates of table tennis in colleges and universities in Liaoning Province investigated by this research, the degree of sports injury is in a compound form, which is mainly mild, supplemented by moderate.5. Distribution of sports injury degree in the injury site.

Table 2.6: sports injury in the injury site statistics

It can be seen from Table 2.6 that among the college table tennis undergraduates in Liaoning Province investigated in this study, "mild" and "moderate" table tennis undergraduates had the most occurrence sites, both of which were six, while "severe" table tennis undergraduates had the least occurrence site, only one.

Above all, in the occurrence place that the degree of sports injury is "mild", not only the occurrence place is much, and the occurrence rate is also the whole highest. The highest probability of sports injury occurred in fingers, with 59 statistical times, accounting for 17.30 %.The waist came in second place with 52 statistics,or15.25percent.Sports injuries of knee joints ranked third, with 37 statistical times, accounting for 10.25 %.The other areas of injury, in order, were the wrist, For shoulder and hip, the statistical times were 30, 15, and 15 times respectively, accounting for 8.80 %, 4.40 % and 4.40 % respectively. Therefore, the "mild" sports injuries are mainly concentrated in the fingers, waist, knee joint, and other parts.

Secondly, although there were also six sites where the degree of sports injury was "moderate", both the overall incidence and the incidence of each site were relatively low. Among them, the occurrence probability of sports injury was the knee joint with 30 statistical times, accounting for 8.80 %, and the neck was ranked second with 29 statistical times, accounting for 8.50 %. The other was the ankle, with 22 statistical times, accounting for 6.45 %, and the waist, thigh anterior muscle group, and thigh posterior muscle group, with 15 statistical times, accounting for 4.40 %.

Finally, the occurrence degree of sports injury was "severe" only in the waist, and accounted for the lowest proportion, with only 7 statistical times, accounting for 2.05 %. On the whole, among the table-tennis undergraduates in colleges and universities in Liaoning Province investigated by this research, the occurrence degree of sports injury is mainly "mild", and "moderate" is the secondary form.

2.1.4 Analysis of sports injury types
(1). Basic information of sports injury types
Table 2.7: frequency statistics of different types of sports injuries

Figure 2.4: percentage distribution of people with different types of sports injuries

According to table 2.7 and Figure 2.4, there are six kinds of sports injuries among table tennis undergraduates in Liaoning Province, which are abrasion, contusion, joint injury, ligament injury, pulled muscle and muscle strain. The total number of statistics is 484. Among the six kinds of sports injuries, "joint injury" accounted for the largest proportion, accounting for more than one-third. The number of statistics was 165 times, accounting for 34.09 %. In the second place is pulled muscle, accounting for nearly one-third of the total, 156 times, accounting for 32.23 %. In third place was a contusion, accounting for more than one-eighth of the total, which was 67 times, accounting for 13.84 %. Other types of sports injuries are more than 5 %, followed by muscle strain, ligament injury, abrasions, statistical times are 37 times, 30 times, 29 times, the proportion is 7.64 %, 6.99 %, 6.20 %. On the whole, in the group of table tennis undergraduates in Liaoning Province, the main types of sports injuries are joint injury and pulled muscle, and a variety of sports injuries coexist with a contusion. The main types of table tennis injuries in college students are joint sprain and muscle strain[7]. Among the sports injuries of table tennis players in China, sprains and strains account for a large proportion of sports injuries[8].

(2) Types of sports injuries and distribution of injury sites
It can be seen from table 2.8 that among the table tennis undergraduates in Liaoning Province investigated by this research institute, "pulled muscle" is the most common type of sports injury, with a total of eight parts. The second is "joint injury", with a total of six“ There are three parts of contusion and muscle rash. There are two ligament injuries. And there's only one scratch.

Table 2.8: statistical table of different injury sites of sports injuries

The characteristics of table tennis determine that participants must be in a "semi-squatting position", and the Angle of the  knee joint is mostly within the range of 30 to 150 degrees. As the knee joint is often in a semi-squatting position and requires a variety of pace changes, the knee joint operates in an irregular alternate way. Make the knee repeatedly flexion, extension and twist, and half squat force, resulting in sports injury. The second place is the anterior thigh muscle group and posterior thigh muscle group, with 30 statistical times, accounting for 5.20 % of the proportion, 17.44 % per capita. Due to the special and harsh requirements of table tennis on knee flexion, a part of the thigh quadriceps femoris undertakes a large load, and the quadriceps femoris is in a state of fatigue due to the repeated contraction of the quadriceps femoris for a long time, which will cause certain damage to the thigh anterior muscle group and thigh posterior muscle group in different degrees. The statistical frequency of ankle and Achilles tendon was 29 times and 18 times respectively, accounting for 16.86 % and 10.47 % respectively. There are four sports injuries in the trunk. The sports injury of the waist accounted for the largest proportion, with 121 statistical times, accounting for 20.97 %, and the per capita sports injury rate was as high as 70.35 %. When completing a perfect technical and tactical movement, it is the result of the connection and coordination between the various muscle groups of the body. Among them, the powerful waist strength is to complete any technical and tactical guarantee. In the actual study and practice, the importance of the relationship between waist and techniques and tactics is well known, but it is easy to be ignored in the practice.

The shoulder was followed by 24 statistical times, accounting  for 4.16 % and 13.95 % per capita. Table tennis players most taboo is the shoulder injury [5]. Because the shoulder hand will directly affect the technical and tactical normal play. And there are a lot of reasons for shoulder injuries. First of all, different playing methods cause different degrees of sports injury to the shoulder. Among them, the incidence of the highest with the circle combined with a fast attack. Moreover, the shoulder joint local load is too large and increases too fast. Third, the daily learning and practice of ignoring the shoulder joint to carry out targeted preparation activities, and almost no relaxation  activities after practice. And the hip is the same thing. The incidence of hip sports injury may be related to the incidence of waist sports injury. Among them, the incidence of the abdomen was the smallest, with only 6 statistical times, accounting for 3.49 % per capita.

There are two sports injuries in the upper limb parts, namely fingers and wrists. Among them, finger sports injury accounted for the largest proportion, the statistical number of 103 times, accounting  for 17.85  %,  and  the per capita sports  injury rate is 59.88 %. The second was wrist, with 48 statistical times, accounting for 8.32 % and 27.91 % per capita. Finally, the head and neck sports injury site are only one, that is, the neck, the statistical number of 37 times, per capita sports injury rate is 21.51 %.

3. conclusions and suggestions
3.1 conclusion
3.1.1 the time of sports injury is mainly concentrated in practice, especially in the waist, knee joint, fingers, and wrist. The nature of sports injury is mainly chronic, and the proportion of acute parts is high. The degree of sports injury is mainly mild, supplemented by moderate. The most common type of sports injury is muscle strain.
3.1.2 the "lower limb" was the most frequently injured part, and the knee joint was the most frequently injured part. The waist is the most important part of the trunk. There are only fingers and wrists in the upper limbs.

3.2 suggestions
3.2.1 table tennis is very important for all kinds of physical fitness. As the most basic sports ability of the body, physical fitness not only lays the foundation of technical and tactical training, but also provides a prerequisite for bearing heavy load and high-intensity training.
3.2.2 practice should be based on their own physique, physical level, reasonable and scientific exercise plan, and the preparation activities before practice and relaxation activities after practice should be reasonable and sufficient.

References

1. YunYan. Research on the Present Situation of Table Tennis Fitness Activities of the Middle-aged and Elderly in Luliang City [D]. Taiyuan, Shanxi University,2011.
2. Yongqiang Yang. Investigation, analysis and prevention of sports injuries of women table tennis players in Shandong [D]. Jinan, Shandong Institute of physical education, 2012.
3. ShaohuiYuan. Cause analysis of sports injury training of national women table tennis team [D]. Beijing, Beijing Sport University, 2007.
4. Rong Li. Mechanism and prevention of knee joint injury of table tennis players [J]. Sports, 2010 (12): 153-154.
5. QieZhu,LifenLiu. Investigation and Research on shoulder injury of Junior Table Tennis Players in Hubei Province [J]. Xianning University Journal, 2009,29 (06): 142-143.
6. ShaofengChen . Investigation on the Status Quo of Athletes' Sports Injury in Sports Vocational and Technical College [J]. Sichuan Sports Science,2012(04):35-38.
7. FengXue. Investigation and Analysis of Common Sports Injuries in Table Tennis Sports of College Students [J]. Journal of  Chifeng University     (Natural Science Edition),2013,29(20):93-95.
8. LiLi, LinziJin. Journal of Henan Normal University (Natural Science Edition),2012,40(02):178-180. (in Chinese)