Much research has been made available that has questioned the current practices of return to play (RTP) testing following ACL reconstruction. Rates of re-injury of the surgical limb and contralateral limb have been increasing and thus typical RTP decision making processes has been questioned. Typically, practitioners have used strength testing and hop testing to determine readiness to RTP. This has included LE strength testing compared to the contralateral limb via leg press or isokinetic testing. Hop testing typically includes single leg vertical, single leg broad jump, triple hop, and triple hop cross-over testing. One common issue with hop testing is that even though we are able to measure explosive power objectively and measuring “how far” they jump, we are not able to get a good appreciation for how they are developing that power. Less frequently tested however, are measures that include rate of force development (RFD) and reactive strength index (RSI) despite current research supporting these measurements.1,2,3 This is likely due to cost of such equipment and lack of availability. BodiTrak has allowed for a cost-effective and efficient way to measure such metrics. Research continues to demonstrate various compensatory patterns athletes use post ACL reconstruction to produce similar power output as the contralateral limb and we are doing our athletes a disservice by not appropriately assessing their return to play readiness.4,5,6,7  The goal of this article is to discuss the faults that underlie the current methods of RTP testing and discuss alternative measures that are obtained with BodiTrak that may help improve our ability to determine an athlete’s readiness to return to sport. Using BodiTrak pressure mapping and force graphs, you can get a more accurate sense of a patient’s current level of function as it relates to ability to safely return to play. One can get a better sense of how an athlete is moving vs. simply measuring the how much.

                          Current methods of RTP testing in most sports medicine facilities consists of various hop tests and comparing to the contralateral limb. While these tests are excellent measures of an athlete’s ability to generate power in a sport specific way, it does not do a great job measuring the process in which athletes develop this force. Our bodies are very intelligent and it will find the path of least resistance to perform the task we are asking of it. One can generate excellent force and power with various compensatory patterns.5,6 With the scoring threshold typically set at 90% of the contralateral limb, it is not uncommon for athletes to “pass” these tests between 4-7 months post ACL reconstruction. However, asymmetries in athletic movement have been shown to be a predictor of future injuries and it is our job as practitioners to detect these. If the movement patterns an athlete uses to generate power is asymmetric, then this would likely increase their injury risk after ACL reconstruction. One common finding in current research is that athlete’s post ACLR perform jumping tasks with decrease knee extensor torque and rely on increased hip extensor and ankle plantar flexor torque on the surgical limb compared to non-surgical limb.5,6,7 It has been determined that a more anterior displacement of center of pressure is related to the  increased hip extensor and ankle plantar flexor moments and decreased knee extensor moments but often produce symmetric overall force.6 This asymmetry produces similar results on tests such as single leg vertical jump, but the athlete is generating this power in vastly different ways.,7 Often the video analysis metrics and knee flexion angle and forward lean of trunk are nearly identical, but their center of pressure is drastically different.6 Without being able to measure this, a practitioner would deem an athlete passes a RTP test, however with BodiTrak pressure mapping one

Figure 1. This is an example of a Division 1 soccer player about 5 months post ACL reconstruction. Pictured is the loading phase of a single leg CMJ. Picture on left is of surgical limb. Pressure distribution is 63% on forefoot and 37% on rearfoot. Picture on right is of non-surgical limb. Pressure distribution is 42% on forefoot and 68% on rearfoot, She had equal jump heights and vertical GRF but creates this force with nearly opposite loading strategies.

                    With research on RTP testing increasing, it has been found that important measures to determine readiness to return to sport include reactive strength index (RSI), reactive  strength index modified (RSIMod)  and rate of force development (RFD).1,2,3,8  These measures are clearly not detectable in traditional RTP testing with hop tests. Isokinetic testing is able to look at RFD, however this is impractical for most clinics due to cost and is not an actual sport specific movement. Using BodiTrak, one can measure RSI, RFD, peak take-off force, peak landing force, and jump height with a single task such as CMJ or a drop jump. By simply measuring their jump height or distance, we fail as practitioners to truly measure the method of force development. Frequently, athletes will produce similar jump heights, for example, however they do so with a slower RFD, decreased RSI as well as the various center of pressure changes as described above. An article in JOSPT by Angelozzi et al. discussed the importance of using RFD as an outcome measure of RTP decision making and found that despite nearly full recovery of strength to pre-injury levels, there was a decreased RFD at 6 months post-op. We are doing an athletes a great disservice by clearing them to RTP due to measures such as strength, jump height, jump distance, etc if the method in which they achieve this is less than adequate and/or asymmetric compared to pre-injury or by measuring the contralateral limb. Below are some examples of testing done with our athletes that demonstrate the various metrics one can use when testing athletes and outline the importance of looking not only at thehow much” an athlete moves and looking at the “how” an athlete moves. Perhaps, we as practitioners need to dig a little deeper with improved RTP testing so we can reduce the risk of re-injury following surgery. Future research needs to continue to look at a more sensitive approach to RTP decision making and this will likely include metrics discussed in this article and can easily be determined using equipment such as BodiTrak pressure mats. Below are excellent examples of how practitioners can utilize BodiTrak to improve their return to play testing protocols.

Figure 2.Patient completing a double leg counter-movement jump. Patient has no pain and a symmetric jump and landing pattern. This is at peak take off force and you can see she is heavily loading her left leg compared to her right (127% BW vs 97%). She has no pain and is 4 weeks after a grade II MCL sprain anxious to return to softball.

Figure 3.This is a heel vs. toe center of pressure displacement graph. Looking at orange line, when this drops “0.0” the patient is more on his heels, when above “0.0” patient is more on his toes. He is 6 months post ACLR on right side. His single leg vertical jump was within 90% LSI. Very different loading strategies, common compensation to hide quad weakness. There were no obvious asymmetries with video analysis. TOP.Left side (non-surgical) single leg vertical jump.BOTTOM.Right side (surgical) single leg vertical jump.

Figure 4. Example of PDF report generated from single leg drop hop test. Included is vertical GRF graph, contact time, jump height, max force, and RSI. This makes for communication with physicians and patient very easy as everything is on one sheet and can be saved in medical record.

Dr. Adam Halseth is a specialist in Physical Therapy based in South Dakota at the Orthopedic Institute.  He’s TPI Level 3 Medical.  You can follow him on Instagram and Twitter at @adamhalseth.


Works Cited

  1. Angelozzi, M., Madama, M., Corsica, C., Calvisi, V., Properzi, G., McCaw, S., et al. (2012, September). Rate of force development as an adjunctive outcome measure for return-to-sport decisions after anterior cruciate liagment reconstruction. Journal of Orthopaedic and Sport Physical Therapy, 42(9), 772-783.
  2. Barker, L. A., Harry, J. R., & Mercer, J. A. (2018, January). Relationships between countermovement jump ground reaction forces and jump height, reactive strength index, and jump time. Journal of Strength and Conditioning Research, 1(32), 248-251.
  3. Flanagan, E. P., Galvin, L., & Harrison, A. J. (2008). Force production and reactive strength capabilities after anterior cruciate ligament reconstruction. Jouranl of Athletic Training, 43(3), 249-257.
  4. Bell, D. R., Trigsted, S. M., Post, E. G., & Walden, C. E. (2016). Hip strength in patients with quadriceps strength deficits after acl reconstruction. Medicine and Science in Sports and Exercise, 48(10), 1886-1892.
  5. Ernst, G., Saliba, E., Diduch, D., Hurwitz, S., & Ball, D. (2000, March). Lower-extremity compensations following anterior cruciate ligament reconstruction. Physical Therapy, 80(3), 251-260.
  6. Sigward, S. M., Chan, M.-S. M., Lin, P. E., Almansouri, S. Y., & Pratt, K. A. (2018, September). Compensatory strategies that reduce knee extensor demand during a bilateral squat change from 3 to 5 months following anterior cruciate ligament reconstruction. Journal of Orthopaedic and Sports Physical Therapy, 48(9), 713-718
  7. Orishimo, K. F., Kremenic, I. J., Mullaney, M. J., McHugh, M. P., & Nicholas, S. J. (2010, June). Adaptations in single-leg hop biomechanics following anterior cruciate ligament reconstruction. Knee Surgery, Sports Traumatology, Athroscopy.
  8. Kipp, K., Kiely, M., &Geiser, C. (2016, May). Reactive strength index modified is a valid measure of explosiveness in collegiate femal volleyball players. Journal of Strength and Conditioning Research, 30(5), 1341-1347.