1. Introduction
nterior cruciate ligament (ACL) injury is the most common knee ligament injury, the mechanism of which is often in non-collision events such as jump-landing, cutting, and deceleration [1]. Basketball is inherently a vertical sport and requires 35-46 jump and landing activities per game. The multidirectional nature of basketball requires constant acceleration and deceleration, forcing athletes to change direction every 2-3 seconds. When landing, the lower limbs are in certain position where the trunk has anterior flexion, hip adduction and internal rotation, 20-30 degree knee flexion, knee valgus, tibia external rotation and pronation of the anterior aspect of the foot, which can lead to complete rupture of the ACL [3]. If the basketball player’s lower limbs be in good condition while shooting, the player has the ability to control the body and balance after successive attacks so that s/he can use the opponent’s defensive gaps to shoot. Moreover, improper alignment after the shot, especially in rebounds, is a risk factor for lower limb injuries, especially the ACL [5, 6]. In most studies, the athletes that are at risk for non-collision ACL injury have not been investigated, and have mostly used expensive biomechanical tools. This study aims to investigate the effect of 6 weeks of progressive jump-landing training on jump shoot accuracy and knee valgus angle of basketball players with Dynamic Knee Valgus (DKV).
2. Methods
This is a quasi-experimental and interventional study with a pre-test/post-test design. The study population consists of all male basketball players with DKV aged 16-20 year in Mazandaran, Iran who had at least 4 years of regular exercise, three times per week. The number of samples was estimated 24 using G power software, considering r2=0.50, test power=0.80 and alpha=0.05 according to previous studies [10, 11]. Subjects were randomly divided into two training and control groups. The training group, in addition to their usual exercises, performed the jump-landing training for 6 weeks, 3 sessions per week, while the control group performed their routine exercises only. After obtaining a written informed consent from the participants, their height and weight were measured using a tape measure and a scale. In order to identify people with DKV, the double-leg Squat test was used. Subjects’ shooting skills were assessed using Boddington’s Basketball Jump Shooting Accuracy Test, and DKV angle was measured using a camera (Nikon D3300, Thailand) and Quinoa software at two sessions.
3. Results
Table 1 shows the demographic characteristics of the two groups. 


The results showed that in the post-test phase, the jump shooting accuracy of the training group was significantly higher compared to the control group (p=0.001) while the DKV angle of the training group was significantly lower compared to the control group (P=0.001). Therefore, it can be said that jump-landing training had a significant effect on these variables.
4. Discussion and Conclusion
The purpose of the present study was to evaluate the effectiveness of 6 weeks of progressive jump-landing training on jump shooting accuracy and knee valgus angle of basketball players with DKV . The results showed that after the training protocol, significant changes were made in the accuracy of jump shooting accuracy and DKV angle. One of the possible reasons for the effectiveness of the program is that the subjects received the necessary instructions and verbal feedback to improve the kinematics of the lower limb, especially the correction of the knee alignment in the frontal plane. Hence, the subjects performed the landing task with better skill after completing the training period. In terms of jump shooting accuracy, the program improved the player’s ability to stop dribbling and change dynamic horizontal displacement into vertical displacement for shooting, in addition to transferring the force from the lower limbs to the trunk and upper limbs. This causes the player to be at the highest point and away from the opponent’s defenders while jumping to shoot, leading to be more successful in scoring. On the other hand, it is believed that plyometric exercises increase the ability to use maximum force in the shortest possible time, stimulate the rapid change of eccentric contraction to concentric contraction, and allow more work to be done in less time. By using the elastic properties of the muscle-tendon unit, these exercises increase the power and, as a result, performance during functional activities [28].

Ethical Considerations
Compliance with ethical guidelines
This study obtained its ethical approval from the Sport Sciences Research Institute of Iran (Code: IR.SSRI.REC.1399.899).

Funding
This study was extracted from the MA. thesis of first author at the Department of Sport Injuries and Corrective Exercises, Faculty of Physical Education and Sport Sciences, University of Guilan, Rasht.

Authors' contributions
All authors contributed equally in preparing this article

Conflicts of interest
The authors declared no conflict of interest.


Refrences

1. Letafatkar A, Rajabi R, Tekamejani EE, Minoonejad H. Effects of perturbation training on knee flexion angle and quadriceps to hamstring cocontraction of female athletes with quadriceps dominance deficit: Pre-post intervention study. Knee. 2015; 22(3):230-6. [DOI:10.1016/j.knee.2015.02.001] [PMID]
2. Boden BP, Torg JS, Knowles SB, Hewett TE. Video analysis of anterior cruciate ligament injury: Abnormalities in hip and ankle kinematics. Am J Sports Med. 2009; 37(2):252-9. [DOI:10.1177/0363546508328107] [PMID]
3. Krosshaug T, Nakamae A, Boden BP, Engebretsen L, Smith G, Slauterbeck JR, et al. Mechanisms of anterior cruciate ligament injury in basketball: Video analysis of 39 cases. Am J Sports Med. 2007; 35(3):359-67. [DOI:10.1177/0363546506293899] [PMID]
4. Herrington L. The effects of 4 weeks of jump training on landing knee valgus and crossover hop performance in female basketball players. J Strength Cond Res. 2010; 24(12):3427-32. [DOI:10.1519/JSC.0b013e3181c1fcd8] [PMID]
5. Mahmoud MH, Elseuofy AAM. The effect of dynamics balance exercises on some kinematics variables and jump shoot accuracy for young basketball players [Internet]. 2010 [Updated 2010 July 15]. Available from: https://www.researchgate.net/profile/Mahmoud-Houssain/publication/320616580_06/data/59f0b8110f7e9beabfca3c23/06.pdf
6. Struzik A, Pietraszewski B, Zawadzki J. Biomechanical analysis of the jump shot in basketball. J Hum Kinet. 2014; 42(1):73-9. [DOI:10.2478/hukin-2014-0062] [PMID] [PMCID]
7. Myer GD, Ford KR, Palumbo JP, Hewett TE. Neuromuscular training improves performance and lower-extremity biomechanics in female athletes. J Strength Cond Res. 2005; 19(1):51-60. [DOI:10.1519/00124278-200502000-00010] [PMID]
8. Herrington L, Munro A, Comfort P. A preliminary study into the effect of jumping-landing training and strength training on frontal plane projection angle. Man Ther. 2015; 20(5):680-5. [DOI:10.1016/j.math.2015.04.009] [PMID]
9. Ahmed TAE. Improving musculoskeletal fitness and the performance enhancement of basketball skills through neuromuscular training program. J Hum Sport Exerc. 2015; 10(3):795-804. [DOI:10.14198/jhse.2015.103.05]
10. Keshavarz L, Letafatkar A, Hadadnezhad M. [Effect of eight weeks of jump-landing exercise on feedforward and feedback activation of selected trunk and lower extremity muscles and lower extremity performance in active females (Persian)]. Med J Tabriz Univ Med Sci. 2018; 40(5):72-82. https://mj.tbzmed.ac.ir/Article/23962
11. Poorkiani M, Letafatkar A, Hadadnejad M, Shojaedin SS. [Effectiveness of eight weeks of progressive jump-landing exercises on performance and dynamic balance of young footballers at the risk of anterior cruciat ligament injury (Persian)]. Sci J Rehabil Med. 2018; 7(3):59-68. [DOI:10.22037/JRM.2018.110673.1446]
12. Bell DR, Vesci BJ, Distefano LJ, Guskiewicz KM, Hirth CJ, Padua DA. Muscle activity and flexibility in individuals with medial knee displacement during the overhead squat. Athl Train Sport Health Care. 2012; 4(3):117-25. [DOI:10.3928/19425864-20110817-03]
13. Powers CM. The influence of abnormal hip mechanics on knee injury: A biomechanical perspective. J Orthop Sports Phys Ther. 2010; 40(2):42-51. [DOI:10.2519/jospt.2010.3337] [PMID]
14. Boddington BJ, Cripps AJ, Scanlan AT, Spiteri T. The validity and reliability of the basketball jump shooting accuracy test. J Sports Sci. 2019; 37(14):1648-54. [DOI:10.1080/02640414.2019.1582138] [PMID]
15. Herrington L, Munro A. Drop jump landing knee valgus angle; Normative data in a physically active population. Phys Ther Sport. 2010; 11(2):56-9. [DOI:10.1016/j.ptsp.2009.11.004] [PMID]
16. Koorosh-Fard N, Ali-Zadeh MH, Rajabi R, Shirzad E. [Effect of feedback corrective exercise on knee valgus and electromyographic activity of lower limb muscles in single leg squat (Persian)]. Arch Rehabil. 2015; 16(2):138-47. http://rehabilitationj.uswr.ac.ir/article-1-1547-en.html
17. Alver BA, Sell K, Deuster PA. NSCA’s essentials of tactical strength and conditioning. Champaign, IL: Human Kinetics; 2017. https://books.google.com/books?id=GHcBDgAAQBAJ&printsec=frontcover&dq
18. Piper TJ, Erdmann LD. Journal C. A 4-step plyometric program.Strength Cond J. 1998; 20(6):72-3. https://journals.lww.com/nsca-scj/Citation/1998/12000/A_4_Step_Plyometric_Program.13.aspx
19. Arazi H, Asadi A. The effect of aquatic and land plyometric training on strength, sprint, and balance in young basketball players. Revistas - J Hum Sport Exerc. 2011; 6(1):101-11. [DOI:10.4100/jhse.2011.61.12]
20. Ilham I, Muhammad Ali M, David Iqroni D. The plyometric training on free throw shooting ability and skills in basketball. J Crit Rev. 2020; 7(14):808-14. [DOI:10.31838/jcr.07.14.144]
21. Elsoufy AAE. Movement science traditional and contemporary. Cairo: DarrFekrah; 2012.
22. Aalhawary R. The effect of dynamic balance exercises on certain kinematic variables and jump shoot accuracy among female basketball players. J Phys Educ Health. 2019; 8(14):41-8. [DOI:10.5281/zenodo.3746167]
23. Asadi A, Arazi H. Effects of high-intensity plyometric training on dynamic balance, agility, vertical jump and sprint performance in young male basketball players. J Sport Health Res. 2012; 4(1):35-44. https://www.researchgate.net/publication/266318427
24. Hadi P, Doewes M, Riyadi S. The influence of low intensity-high intensity plyometric training and hand-eye coordination on jump shoot ability in basketball players of bhinneka solo club: Randomized control trial. Budapest Int Res Crit Linguist Educ J. 2020; 3(1):514-22. [DOI:10.33258/birle.v3i1.847]
25. Schwameder H. Effect of a neuromuscular home training program on Dynamic Knee Valgus (DKV) in lateral single-leg landings. ISBS Proc Arch. 2020; 38(1):186. https://commons.nmu.edu/isbs/vol38/iss1/186/
26. Karimizadeh Ardakani M, Wikstrom EA, Minoonejad H, Rajabi R, Sharifnezhad A. Hop-stabilization training and landing biomechanics in athletes with chronic ankle instability: A randomized controlled trial. J Athl Train. 2019; 54(12):1296-303. [DOI:10.4085/1062-6050-550-17] [PMID] [PMCID]
27. Saki F, Madhosh M. [Effect of eight weeks plyometric training on pelvic and knee alignment in female with dynamic knee valgus (Persian)]. J Res Sport Rehabil. 2019; 6(12):21-9. [DOI:10.22084/RSR.2019.17644.1415]
28. Chmielewski TL, Myer GD, Kauffman D, Tillman SM. Plyometric exercise in the rehabilitation of athletes: Physiological responses and clinical application. J Orthop Sports Phys Ther. 2006; 36(5):308-19. [DOI:10.2519/jospt.2006.2013] [PMID]
29. Distefano LJ, Blackburn JT, Marshall SW, Guskiewicz KM, Garrett WE, Padua DA. Effects of an age-specific anterior cruciate ligament injury prevention program on lower extremity biomechanics in children. Am J Sports Med. 2011; 39(5):949-57. [DOI:10.1177/0363546510392015] [PMID]
30. Myer GD, Ford KR, Hewett TE. Methodological approaches and rationale for training to prevent anterior cruciate ligament injuries in female athletes. Scand J Med Sci Sports. 2004; 14(5):275-85. [DOI:10.1111/j.1600-0838.2004.00410.x] [PMID]
31. Pollard CD, Sigward SM, Ota S, Langford K, Powers CM. The influence of in-season injury prevention training on lower-extremity kinematics during landing in female soccer players. Clin J Sport Med. 2006; 16(3):223-7. [DOI:10.1097/00042752-200605000-00006] [PMID]
32. McCann R, Cortes N, Van Lunen B, Greska E, Ringleb S, Onate J. Neuromuscular changes following an injury prevention program for ACL injuries. Int J Athl Ther Train. 2011; 16(4):16-20. [DOI:10.1123/ijatt.16.4.16]
33. Aagaard P. The use of eccentric strength training to enhance maximal muscle strength, explosive force (RDF) and muscular power-consequences for athletic performance. Open Sports Sci J. 2010; 3:52-5. [DOI:10.2174/1875399X010030100052]
34. Rimmer E, Sleivert G. Effects of a plyometrics intervention program on sprint performance. J Strength Cond Res. 2000; 14(3):295-301. [DOI:10.1519/00124278-200008000-00009]
35. Stickler L, Goehring M, Kinne B. The impact of hip strengthening and/or neuromuscular control on frontal plane knee kinematics and kinetics in females: A systematic review. Phys Ther Rev. 2016; 21(1):10-6. [DOI:10.1080/10833196.2016.1214357]