Plyometrics for ACLR: The Bridge between the Clinic and Return-to-Sport
Part 2 of 3 Things I Learned from Mick Hughes' ACLR Webinar
Plyometrics officially made their debut in the 2023 ACL Aspetar Guidelines. Its inclusion was based on the four studies and their respective outcomes. If you are not familiar with plyometrics, they were first introduced publicly by Professor Yuri Verkrhonshansky in 1964 as a means of increasing speed and vertical jump height. It involves the rapid movements of the athlete’s center of gravity in all directions (vertical, diagonal, and lateral).
Why are plyometrics suddenly being brought up? First, it appears to significantly improve outcomes regarding pain and knee function at 6 months and 12 months when compared to conventional strengthening programs.
Specificity is a fundamental principle for successful adaptation and preparation for sport. It is expected, then, that the combination of both eccentric (lengthening) and plyometric exercises would improve a patient’s ability to return to sport compared to either exercise type alone. It is quite well established within the literature that eccentric exercises, when compared to concentric exercises, lead to greater gains in muscle strength and hypertrophy. This is observed in greater growth in the cross-sectional areas of all muscle fiber types between Type I and Type IIb. Plyometric exercises are known to stress the stretch-shortening cycle of tendons and the nervous system. It may also introduce movements that gym exercises cannot provide, such as lateral trunk movements and valgus and compression forces on the limbs. The dynamic nature of plyometrics teaches the healing knee how to stabilize itself when presented with a perturbation.
As sub-optimal landing mechanics such as excessive valgus and lateral trunk leaning have been attributed to ACL injury, training the body to stabilize itself in these vulnerable positions may have significant benefits for decreasing pain and improving function. This “teaching” involves training the nervous system's postural ability (afferent and efferent paths) to anticipate movement challenges and stiffen the lower limb muscles to stabilize landing. Indeed, the following charts below by Risberg et al. 2009 (Oslo, Norway) demonstrate significant differences in pain and function at the 12-month mark between the strength group (SE) versus the plyometric (NE) group.
Yet there is a greater role that plyometrics may play in return-to-sport for ACLRs and that is in the psychological realm. We have to look back to Arden et al.’s 2011 meta-analysis to understand. After collating 48 studies (5770 patients) around 3.5 years post operation they found a large gap between athletes that scored high in post-ACLR outcome measures and their actual return to sport. This means that even though ~90% of the patients scored a normal knee function, only 44% of them returned back to their original sport. Why was this the case? The authors go on to suggest that, perhaps, the fear of re-injury was to blame.
Fear of re-injury can be viewed as an emotional state but also an interpretation of the knee’s readiness by the brain. If the brain does not feel that the knee is sufficiently ready to generate sufficient force to stiffen the knee when momentarily off-balance, it will express itself in emotions of fear, anxiety, and hesitancy to play. Is there a mind-body connection at play here?
A 2021 study by Zarzycki et al. from Arcadia University took 66 athletes that were one to two years post-ACLR and enrolled them in a new training program combined with plyometrics, agility, and training. Psychological readiness was determined via the ACL-RSI measure. 59% of the study’s athletes improved their psychological readiness and self-reported function outcomes after 10 sessions of training. However there was no difference between their return to sport rates This suggests that even after a formal rehabilitation program, athletes can psychologically and physically benefit from plyometric training but there may be a window of opportunity for returning to sport.
Identifying key findings for the progression of plyometric exercises includes control of movements, positional awareness, the ability to anticipate perturbations, the ability to maintain balance before the introduction of new perturbations. Guidelines suggest initiation of plyometrics at 12 weeks post surgery. Adequate rest between sets and training days is important to maintaining the health of the tendon and joints. Ultimately, Mick Hughes’ second pearl is this— Use plyometrics when you can! It is easy for the athlete to do at home and leads to significant improvements in return-to-sport.
References:
Risberg, M. A., & Holm, I. (2009). The long-term effect of 2 postoperative rehabilitation programs after anterior cruciate ligament reconstruction: a randomized controlled clinical trial with 2 years of follow-up. The American journal of sports medicine, 37(10), 1958-1966.
Risberg, M. A., Holm, I., Myklebust, G., & Engebretsen, L. (2007). Neuromuscular training versus strength training during first 6 months after anterior cruciate ligament reconstruction: a randomized clinical trial. Physical therapy, 87(6), 737-750.
Kotsifaki, R., Korakakis, V., King, E., Barbosa, O., Maree, D., Pantouveris, M., ... & Whiteley, R. (2023). Aspetar clinical practice guideline on rehabilitation after anterior cruciate ligament reconstruction. British Journal of Sports Medicine, 57(9), 500-514.
Zarzycki, R., Arhos, E., Failla, M., Capin, J., Smith, A. H., & Snyder-Mackler, L. (2021). Association of the psychological response to the ACL-SPORTS Training Program and self-reported function at 2 years after anterior cruciate ligament reconstruction. The American journal of sports medicine, 49(13), 3495-3501.
Chmielewski, T. L., George, S. Z., Tillman, S. M., Moser, M. W., Lentz, T. A., Indelicato, P. A., ... & Leeuwenburgh, C. (2016). Low-versus high-intensity plyometric exercise during rehabilitation after anterior cruciate ligament reconstruction. The American journal of sports medicine, 44(3), 609-617.
Kasmi, S., Zouhal, H., Hammami, R., Clark, C. C., Hackney, A. C., Hammami, A., ... & Ounis, O. B. (2021). The effects of eccentric and plyometric training programs and their combination on stability and the functional performance in the post-ACL-surgical rehabilitation period of elite female athletes. Frontiers in Physiology, 12, 688385.
Ardern, C. L., Webster, K. E., Taylor, N. F., & Feller, J. A. (2011). Return to sport following anterior cruciate ligament reconstruction surgery: a systematic review and meta-analysis of the state of play. British journal of sports medicine, 45(7), 596-606.