1. Plyometric Training and its Role in ACL Prevention in Adolescents Julie Nellis, PT, MPT, CSCS Keith May, PT, DPT, SCS, ATC, CSCS

2. Objectives • Recognize the mechanisms and economic impact of ACL injuries • Understand the current research as it relates to ACL injuries • Discuss how plyometrics can be used to help decrease the incidence of ACL injuries • Develop an ACL prevention program that is supported by the most current literature

3. Anatomy

4. Incidence of Serious Knee Injuries • 250,000 ACL injuries occur in the US annually • Incidence is approximately 5x higher in female athletes than males. (AJSM 1992,1995; Phys & Sports Med 1985,1987) • 1 in 100 high school females annually • 2/3 are non-contact injuries (JBJS 1983; AJSM 1999)

5. Financial Impact • 83,000 ACL reconstructions annually • The approximate cost is $17,000 per procedure • The financial impact is 1.5 billion dollars (Boden 2000)

6. Mechanism of ACL Injuries • Valgus position of the knee • Sudden deceleration isolated quad contraction • Outside cut varus internal rotation of the knee • Any maneuver that creates anterior tibial shear forces

7. Research • Olsen AJSM 2004 • Analysis of ACL injuries of 20 different female handball players • 16/20 forceful valgus and rotation • Chappett AJSM 2002 • anterior shear force women greater than men (difference 0.2 x BW)

8. Example

9. Example

10. Theories to Explain Increased Incidence Structural • Wider pelvis • Q-angle • Joint laxity • Narrow intercondylar notch Training Differences • Strength • Technique • Coaching Hormonal – Estrogen • Collagen Strength • Joint Laxity

11. What are the Differences? • Time to peak torque hamstrings • Recruitment order • Muscle strength • Technique (AJSM 1996)

12. Time to Peak Torque Hamstrings Male athletes vs male non-athletes 328-443 msec Female athletes vs male non- athletes 430-443 msec (Huston & Wojlys AJSM 1996) • Females have a longer electromechanical delay then males • Males hamstring muscles fire faster

13. Recruitment Order Male athletes: Hamstrings Quads Gastroc Female athletes: Quads Hamstrings Gastroc (Huston & Wojlys AJSM 1996)

14. Muscle Strength • Female athletes = female controls (Huston & Wojlys AJSM 1996) • Quad/hamstring ratio 47% in females • Quad/hamstring ratio 67% in males

15. Males Flex knee 20-30° when landing Hamstrings control landing Proper force attenuation Females Straight-legged to 10° flexed posture when landing Attempt to use quads to control landing Causes valgus knee position Use hamstrings and hip extensors less Move through deceleration faster Technique

16. Components of ACL Prevention • Flexibility • Strengthening • Plyometric training

17. Flexibility • Stretching major muscle groups upper and lower extremities • Hold each stretch 30 seconds • Repeat minimum 2 times

18. Strengthening • An important adjunct to any plyometric and flexibility training program • Selection of exercise is individualistic but it must include: • Intensity • Overload • Progression

19. Essentials of Plyometric Training • Body positioning • Correct posture • Jump straight up • Soft landing • Balance

20. Plyometric Intensity • Points of contact • Single leg vs. double leg • Speed • Drill intensity • Height • Center of gravity • Participant’s weight • Joint stress

21. Plyometrics • An effective plyometric program should: • peak landing forces • magnitude of moments at the knee • knee flexion angle • lower extremity strength • vertical jump height • Improve landing mechanics

22. Plyometic Program Phase I Technique Phase II Fundamentals Phase III Performance

23. Examples of Plyometrics • Phase I: Tuck Jump • Phase II: Scissor Jump • Phase III: Jump up, down, 180, vertical

24. Squat Jump

25. Squat Jump • Keys to jump • Squat position with chest and head up • Back straight • Jump up reaching as high as possible • Return to same squat position • Mistakes to correct • Touching forward/off balance • Knees going into valgus on take off

26. Scissor Jump

27. Scissor Jump • Keys to jump • Start in lunge position with front knee directly over the ankle • Alternate legs by pushing off the front leg • Land with the opposite leg bent in front • Mistakes to correct • Land with “wobbly” knees or knees extended past the front ankle • Switches leg without power or jumps with minimal height • Lands straight legged

28. Jump Up, Down, 180, Vertical

29. Jump Up, Down, 180, Vertical • Keys to jump • Double foot jump • Land into deep crouched position and immediately jump down from the platform • Land into deep crouched position immediately perform 180 jump, landing in deep crouched position • Perform maximal vertical jump again landing in the deep crouched position • Hold for 5 seconds

30. Jump Up, Down, 180, Vertical • Mistakes to correct • Not landing each jump deep • One foot leads on the jump down

31. Results in Injury Prevention • Henning 1985 • Substitute rounded turn off a bent knee for the pivot/cut • Landing on a bent knee • Three step stop with a bent knee • 89% reduction in ACL injury rate

32. Results in Injury Prevention • Hewett 1996 • 3 part program of stretching, plyometrics and strength training • peak landing forces 22% • varus and valgus movements at the knee by 40-50% • hamstring power and strength 44% dominant side and 21% non-dominant side • hamstring to quad peak torque ratio 26% non-dominant side and 13% dominant side

33. Results in Injury Prevention • Mandelbaum 2000 • Neuromuscular and proprioceptive performance program • 2-3 x week over 2000-01 soccer season • 88% decrease in ACL injuries

34. Questions Thank You!! Keith.May@choa.org Julie.Nellis@choa.org