Relevance for the Sport
Injuries to the anterior cruciate ligament (ACL) are relatively common, particularly in sports that involve abrupt stops, rapid changes in direction, and jumps. Examples include, but are not limited to, team and individual sports like soccer, basketball, football, alpine skiing, and gymnastics.
This highlights the importance of high-quality rehabilitation for elite athletes whose primary goal is to return to their original level of performance. In recent years, there has been a shift from time-based to criterion-based decision making in the return to sports (RTS) process after lower limb injuries like ACL ruptures or ankle sprains (1). Hop tests like the 30 seconds Side Hop (30sSH) are commonly used due to their practicality and proximity to the mechanism of injury (2), thus having evolved as a tool to objectively assess functional performance after injuries (1).
Moreover, single-legged tests are popular to quantify side-to-side performance differences by calculating the limb symmetry index (LSI). LSI scores > 90% are regarded as a standard in uninjured subjects and in injured patients to complete rehabilitation (2-6).
Information
The LSI is defined as = (involved limb value / uninvolved limb value)*100.
Asymmetries between limbs might be a risk factor for future injuries in uninjured athletes (7) and for subsequent injuries in athletes that have previously been injured, both in the ipsilateral and contralateral leg (8).
Hop tests such as the 30sSH are of great value to trainers and therapists in guiding their athletes and patients successfully through the rehabilitation process.
Test Protocol
The ReGo 30 Seconds Side Hop Test is a single-legged hop test conducted on a level surface, with both lateral and medial movements. Participants perform continuous hops sideways and return over a 40 cm distance within a 30-second timeframe. Throughout the test, hands must remain on the hips. Fig-1 shows the test procedure in detail.
The primary objective is to achieve the maximum number of hops possible within the designated 30 seconds, hence challenging knee stability in the frontal plane under fatigue (9).
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Any hops that land outside the 40 cm mark or involve the free foot touching the ground for balance are considered invalid.
Follow the link for a more detailed test description of the ReGo 30 Seconds Side Hop Test, including a step-by-step guide and an instruction video.
Outcome Parameters
The main outcome parameter of the ReGo 30 Seconds Side Hop Test is Total Hop Count (Fig-2). This parameter indicates how many absolute jumps an athlete can perform in 30 seconds and allows a side-by-side comparison, providing a general overview of an athlete’s performance.
In this example, hop performance of the right and left leg is similar with 57 and 58 hops, respectively. This corresponds to a LSI score of 98%, which is above the recommended 90% level mentioned above.
While assessing the number of valid jumps in the 30sSH is a simple method that does not require much equipment, it is lacking qualitative parameters, like load and ground reactions forces (1, 10). For instance, an athlete could achieve the same number of valid jumps with the left and right leg, but other parameters, such as the ground contact time or flight time could differ (1, 10). For this reason, analyzing measures related to movement quality is considered the gold-standard for hop testing (2).
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Consider movement quality measures to gain a deeper understanding of how an athlete achieved a certain performance.
The ReGo parameter Mean Rebound Pressure Distribution (Fig-3, left) displays the plantar pressure distribution as a mean of all rebounds, while the Mean Rebound Load Distribution (Fig-3, right) illustrates the accumulated foot loads in relation to six foot segments: Medial and lateral of forefoot, midfoot and hindfoot, respectively.
Although the subject in the current example achieved almost the same number of hops, the Mean Rebound Pressure and Load Distribution show asymmetries: During rebounds, there is higher pressure under the lateral midfoot on the left as opposed to medial forefoot on the right.
In addition, the Mean Longitudinal and Transversal Rebound Points (Fig-4) provide further insight into an athlete’s hopping and landing behavior: They display the average position of the center of pressure (COP) during the rebound phase in anterior-posterior and medio-lateral direction, thus indicating if load is shifted more to the forefoot, to the hindfoot, medially or laterally. The values are normalized by sensor insole length and width, respectively: The hindfoot and lateral side start with 0, the forefoot and medial side end with 1.
In the present example, the subject loads the forefoot more on the right compared to the left side. Additionally, the transversal rebound point on the right is more medially oriented than on the left. This confirms what you could already guess from the pressure distribution: on the left side, the subject primarily loads the lateral midfoot, compared to the medial forefoot on the right.
During jump landings, higher pressure is typically found under the great toe, or hallux (11). Therefore, the available data indicates that the subject shows a typical landing pattern on the right, but is compensating on the left side. The subject’s injury history confirms an ankle injury on the left as a possible cause. Further tests should be carried out to rule out other causes and to assess the progress of treatment to improve ankle stability.
In essence, these metrics help trainers and therapists in identifying loading asymmetries between the injured and uninjured leg and hence give insight into a patient’s individual compensation strategy.
Unfortunately, there is little evidence on these measures so far. Therefore, further research is necessary to determine the relevance of foot loading patterns and COP variables during jump landings in ACL patients, as well as their potential impact on future injury risk.
Tips for Trainers and Therapists
Here are a few practical tips regarding the use of symmetry indexes, like the LSI score, to guide RTS decision-making:
First, the LSI score might not be affected in unilateral, but in bilateral jumps in patients after ACLR: Baumgart et al. (12), Meyer et al. (13) and Urhausen et al. (14) demonstrated that patients unloaded their operated compared to their non-operated leg in bilateral jumps. This loading asymmetry was not present in unilateral jump tasks, however. Single-legged jump tests might be more suitable to expose inter-joint compensation strategies, while bilateral jumps could be used to detect loading asymmetries (14, 15).
Therefore, a meaningful test battery for RTS should include several unilateral and bilateral jump and hop tests (16). Research by Gustavsson et al. (2006) confirms that a battery of hop tests can better discriminate hop performance between the uninjured and injured leg than single tests (9).
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Use a test battery of multiple bilateral and unilateral jump and hop tests covering different planes.
Apart from the 30sSH, relevant ReGo tests for RTS are:
Second, the LSI score could overestimate hopping performance, given that deficits following surgery are frequently observed in the uninjured leg as well as in the injured limb (17-19). Research conducted by Gokeler et al. (19) revealed that athletes who have had ACLR exhibit impairments in hop tests on both sides when compared to age- and sex-matched normative data from healthy controls. For this reason, it is very helpful if baseline data of regular screenings are available. However, due to the time and resources needed this is not always possible.
The estimated pre-injury capacity (EPIC) score offers an alternative to the LSI score, which uses the uninvolved limb after injury as a control. On the contrary, the EPIC score compares the uninvolved limb preoperatively to the involved side at 6 months after ACLR (20). Preliminary data from Wellsandt et al. (2017) showed that the EPIC score was superior in predicting second ACL injuries compared to the post-operative LSI score (20). This has been confirmed by subsequent studies (21, 22).
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Use baseline data or the EPIC score as a reference standard for symmetry.
In summary, a comprehensive RTS assessment should incorporate both unilateral and bilateral functional tests. The EPIC score provides a more accurate reflection of recovery compared to the LSI score, particularly in predicting ACL re-injury risks.
Comments on Measurement Equipment
The analysis of the 30sSH has historically been performed by manually counting the number of hops or by using video analysis.
On the other hand, the introduction of the ReGo sensor insoles to hop and jump testing marks a significant advancement for trainers and therapists, as they provide an affordable, valid, and reliable means of gaining comprehensive insights into the biomechanics of jumping and landing. They measure various aspects apart from the primary outcome Total Hop Count, such as landing quality metrics like COP variability.Thus, the ReGo system enables a detailed analysis of how an athlete achieved their performance and identifies specific areas for personalized training interventions.
The following table (Tab-1) details product specifications to help trainers and therapists gain useful insights from the sports performance and functional tests.
| Function/Feature | Description |
| Automatic report generation | Pattern recognition and advanced live processing allows ad-hoc computation of the complete set of test results. |
| Mobile and offline use | Tests can be performed anywhere and anytime as the measurement system is not limited to laboratory use. Also, tests can be performed offline. |
| Documentation and reporting | Labels can be used to identify athletes and test results, and a reporting interface allows users to generate individual and team reports. Individual reports are for one athlete and optionally cover multiple tests such that intra-individual performance development over time can be evaluated. Team reports can be created for an infinite number of athletes and serve to compare inter-individual performance. |
| Reference database | Reference data is available, covering norm data of numerous sports and age groups as well as female and male athletes. Reference data helps to classify the performance of your own athletes compared to average and best outcomes in the sport or age group, hence identifying strengths and weaknesses as a starting point for individualized training programs. |
Essentially, the ReGo system helps trainers and therapists by improving access to biomechanical hop testing metrics, making it a crucial tool to objectivize RTS protocols.
Literature
- Davies, W. T., Myer, G. D., Read, P. J. (2019). Is It Time We Better Understood the Tests We are Using for Return to Sport Decision Making Following ACL Reconstruction? A Critical Review of the Hop Tests. Sports Medicine, 50, 485-495.
- Moser, N., Bloch, H. (2015). Return-to-Competition: Testmanual zur Beurteilung der Spielfähigkeit nach Ruptur des vorderen Kreuzbands (1.0). Ihre gesetzliche Unfallversicherung (VBG).
- Fitzgerald, J., Axe, M., Snyder-Mackler, L. (2000). A decision-making for returning patients to high-level activity with non-operative treatment after anterior cruciate ligament rupture. Knee Surg Sports Traumatol Arthrosc, 8, 76-82.
- Munro, A., Herrington, L. (2011). Between session reliability of four hop tests and the agility t test. Strength Cond Res, 25(5), 1470-7.
- Keller, M., Kurz, E., Schmidtlein, O., Welsch, G., Anders, C. (2016). Interdisziplinäre Beurteilungskriterien für die Rehabilitation nach Verletzungen an der unteren Extremität: Ein funktionsbasierter Return to Activity Algorithmus. Sportverletz. Sportschaden, 30, 38-49.
- Adams, D., Logerstedt, D. S., Hunter-Giordano, A., Axe, M. J., Snyder-Mackler, L. (2012). Current concepts for anterior cruciate ligament reconstruction: A criterion-based rehabilitation progression. J. Orthop. Sports Phys. Ther, 42, 601–614.
- Manske, R., Reiman, M. (2013). Functional Performance Testing for Power and Return to Sports. Sports Health, 5(3), 244-250.
- Paterno, M. V., Schmitt, L. C., Ford, K. R., Rauh, M. J., Myer, G. D., Huang, B., Hewett, T. E. (2010). Biomechanical Measures During Landing and Postural Stability Predict Second Anterior Cruciate Ligament Injury After Anterior Cruciate Ligament Reconstruction and Return to Sport. Am J Sports Med, 38(10), 1968–1978.
- Gustavsson, A., Neeter, C., Thomée, P., Grävare Silbernagel, K., Augustsson, J., Thomée, R., Karlsson, J. (2006). A test battery for evaluating hop performance in patients with an ACL injury and patients who have undergone ACL reconstruction. Knee Surg Sports Traumatol Arthrosc, 14(8), 778-88.
- Kotsifaki, A., Korakakis, V., Whiteley, R., van Rossom, S., Jonkers, I. (2020). Measuring only hop distance during single leg hop testing is insufficient to detect deficits in knee function after ACL reconstruction: a systematic review and meta-analysis. Br J Sports Med, 54, 139-153.
- Wong, P., Chamari, K., Chaouachi, Mao, D. W., Wisløff, U., Hong, Y. (2007). Difference in plantar pressure between the preferred and non-preferred feet in four soccer-related movements. British Journal of Sports Medicine 2007, 41, 84-92.
- Baumgart, C., Schubert, M., Hoppe, M., Gokeler, A., Freiwald, J. (2017). Do ground reaction forces during unilateral and bilateral movements exhibit compensation strategies following ACL reconstruction? Knee Surg Sports Traumatol Arthrosc, 25, 1385-1394.
- Meyer, C. A. G., Gette, P., Mouton, C., Seil, R., Theisen, D. (2018). Side‑to‑side asymmetries in landing mechanics from a drop vertical jump test are not related to asymmetries in knee joint laxity following anterior cruciate ligament reconstruction. Knee Surgery, Sports Traumatology, Arthroscopy, 26, 381-390.
- Urhausen, A. P., Gette, P., Mouton, C., Seil, R., Cabri, J., Theissen, D. (2022). An in-depth Analysis of the Side Hop Test in Patients 9 Months Following Anterior Cruciate Ligament Reconstruction. GERMAN JOURNAL OF SPORTS MEDICINE, 73, 17-23.
- Oberländer, D. K., Brüggemann, G.-P., Höher, J., Karamanidis, K. (2013). Altered landing mechanics in ACL-reconstructed patients. Med Sci Sports Exerc ., 45(3), 506-13.
- Van Melick, N., van Cingel, R. E. H., Brooijmans, F., Neeter, C., van Tienen, T., Hullegie, W., Nijhuis-van der Sanden, M. W. G. (2016). Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus. Br J Sports Med, 50, 1506–1515.
- Fältström, A., Hagglund, M., Kvist, J. (2017). Functional Performance Among Active Female Soccer Players After Unilateral Primary Anterior Cruciate Ligament Reconstruction Compared With Knee-Healthy Controls. Am J Sports Med, 45, 377-385.
- Gokeler, A., Welling, W., Benjaminse, A., Lemmink, K., Seil, R., Zaffagnini, S. (2017). A critical analysis of limb symmetry indices of hop tests in athletes after anterior cruciate ligament reconstruction: A case control study. Orthop Traumatol Surg Res, 103, 947-951.
- Wren, T., Mueske, N., Brophy, C., Pace, J., Katzel, M., Edison, B., Vandenberg, C., Zaslow, T. (2018). Hop Distance Symmetry Does Not Indicate Normal Landing Biomechanics in Adolescent Athletes With Recent Anterior Cruciate Ligament Reconstruction. J Orthop Sports Phys Ther, 48, 622-629.
- Wellsandt, E., Failla, M. J., Snyder-Mackler, L. (2017). Limb Symmetry Indexes Can Overestimate Knee Function After Anterior Cruciate Ligament Injury. J Orthop Sports Phys Ther, 47(5), 334-338.
- Zore, M. R., Kregar, V. N., Hussein, M. (2021). Pre- and Post-Operative Limb Symmetry Indexes and Estimated Preinjury Capacity Index of Muscle Strength as Predictive Factors for the Risk of ACL Reinjury: A Retrospective Cohort Study of Athletes after ACLR. Applied Sciences, 11(8), 3498.
- Glattke, K. E., Tummala, S. V., Chhabra, A. (2022). Anterior Cruciate Ligament Reconstruction Recovery and Rehabilitation: A Systematic Review. J Bone Joint Surg Am, 104(8), 739-754.
