Relevance for the sport
Jumping is a fundamental part of many sports, such as basketball and volleyball. Besides these, many other sports incorporate phases of flight within their movement patterns, involving various take-off and landing positions. For example, running and sprinting also consist of individual take-offs, flight phases, and landings.
Hop tests are often used to evaluate the quality of jumping and landing movements in athletes. They can identify deficits and asymmetries in these movements, which may lead to reduced athletic performance or even injuries (1).
Furthermore, hop tests are used to assess when an athlete is ready to return to sports (RTS) after an injury, particularly knee injuries such as anterior cruciate ligament (ACL) ruptures. As part of regular screenings, hop tests can support RTS decision making by providing baseline values.
The purpose of hop testing in the RTS process is to use functional performance outcomes as a criteria for clearing an athlete for returning to sports activity, rather than solely basing the decision on the time passed after the trauma incident or the surgery. Due to the risk of a repeated ACL rupture and with regards to a successful RTS process, it is important to have objective criteria at hand which guide clinicians and therapists on whether or not it is safe for an athlete to return to sports.
Information
The LSI is defined as the hop performance of the injured leg related to the performance of the uninjured leg, indicated in percentage.
For evaluating the performance of the injured leg compared to the uninjured leg in hop tests, the limb symmetry index (LSI) is calculated. Literature on state of the science suggests that athletes achieve a LSI score > 90% to complete rehabilitation and return to sports activity (2-6).
Test protocol
The ReGo Balance Front Hop test involves a single-legged hop over a distance of 40 cm on a flat surface (Fig-1). Each leg is tested with three repetitions. During the test, hands must rest on the hips.
The test challenges the lower extremities with both concentric and eccentric jump loads. The primary goal is to execute the hop with proper landing mechanics and maintain balance for 3 seconds after landing.
Information
The results of the three repetitions are averaged.
A trial is considered invalid if the landing occurs inside the 40 cm mark, balance is not maintained during the holding phase, or the free foot touches the ground.
Follow the link for a more detailed test description of the ReGo Balance Front Hop test, including a step-by-step guide and an instruction video.
Outcome Parameters
The primary outcome of the ReGo Balance Front Hop test is landing quality, represented by the Balance Point and the Sway Area (Fig-2).
The Balance Point is the mean center of pressure (COP) point of the landing foot during the balance phase. The balance phase starts 0.5 seconds after the initial foot contact and encompasses a period of 3.0 seconds. It shows the average position at which the COP transitions to the ground and indicates if load is shifted more to the forefoot, to the hindfoot, medially or laterally.
The Sway Area is the area of an ellipse enclosing 95 % of all COP data points during the balance phase. The outcome metric indicates the level of stability of the foot-to-ground contact during the 3.0 seconds balance phase.
Both the Balance Point and the Sway Area are also given as numerical values, including the L/R difference percentage. The values of the Longitudinal and Transversal Balance Points 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.
Research shows that static and dynamic postural stability measures are impaired after ACL reconstruction (ACLR) compared to the non-operated leg and to matched controls for up to two years after surgery (7-9). Furthermore, postural asymmetries can exist despite the fact that single-leg hop performance is symmetric (9).
Further outcome parameters related to the ability to display a balanced landing are the Time to Stabilization (TTS) and the Stabilization Progression (Fig-3). The TTS is the time passed for the traveling velocity of the COP to fall below the stabilization limit. The Stabilization Progression shows the traveling velocity of the COP as horizontal bars from the moment of landing (bottom) to the end of the balance phase (top).
Information
Note the reference data for Balance Point, Sway Area and Time to Stabilization in Fig-2 and Fig-3:
The vertical gray bar indicates the best reference value. The gray zone indicates the 1st – 3rd quartile, which contains 50% of all measured reference values.
The reference database is being created in ongoing athlete screenings, including different sports, performance levels and age groups, under highly controlled conditions.
Current literature shows that athletes who had ACLR, have an increased TTS after jump landings (10). Additionally, there is evidence that athletes with a higher TTS during jump landings are at an increased risk of ACL rupture (11).
In conclusion, injuries like ACL ruptures are related to deficits in stability after jump landings. However, more research is necessary to determine if parameters like Sway Area or the TTS can be used as a criterion to clear athletes for sports after ACLR.
Example
Let’s take a look at a real data example: In Vid-1, you can see a young wrestling athlete performing the balance front hop test. First, the three repetitions on the left leg are displayed (from left to right), followed by three repetitions on the right leg.
During the first repetition on the left leg, the athlete leans to the left with his torso, and the landing foot appears unstable but does not completely leave the ground. On the second and third repetitions on the left leg, the torso is more centered over the lower body, but the knee appears unstable.
On the first repetition on the right leg, the torso is not centered over the lower body, and the heel of the jumping foot leaves the ground after landing. In the second repetition, the torso is more centered, but the jumping foot is not completely on the ground either. The third repetition on the right leg does not show any striking deficits.
In essence, there are slight to moderate deficits on both the left and right side: While the knee is more unstable on the left, the heel leaving the ground is the greater issue on the right side.
Now, let’s look at the outcome data of this test (Fig-4): The Balance Point on the left is located slightly further forward and more laterally than the right. However, the Sway Area on the left is significantly larger than on the right, with a 47% difference.
Additionally, the Time to Stabilization is greater on the left side as well, with a difference of just under 14%. The Stabilization Progression further reveals that there is more movement of the COP over the entire duration of the balance phase on the left.
In summary, the data clearly shows deficits of the athlete’s landing stability on the left side, compared to the right. The objective outcome data of the test reveal more information than the video, indicating that the athlete could be at risk for future injuries as outlined earlier. As research on the significance of these parameters on injury risks is still ongoing, further assessments should be carried out to determine the underlying causes together with a detailed analysis of the athlete’s injury history.
Tips for Trainers and Therapists
Here are some practical tips and considerations to keep in mind in case you are starting to implement hop tests in your work with athletes: First, a single test should not clear an athlete after an injury. Therefore, it is recommended to perform a test battery consisting of several tests. However, current evidence suggests that using multiple single-leg hop tests does not provide more information on deficits in knee function than using just two tests (12). Instead, the use of other hop tests in different planes, for instance vertical jumps and side hops, might reveal greater information about the current knee function (12).
Information
Perform multiple tests which cover different planes to reveal limitations in knee function.
Further ReGo tests that can be used in the RTS process are:
Second, the key outcome parameter of a hop test and the resulting LSI value should not be the only measure used for RTS decision making (12). There is evidence that symmetry of performance outcomes can be high, while symmetry of movement quality measures might be considerably lower (13). For this reason, other metrics, especially those related to movement quality, should be included in order to make objective and informed decisions.
Information
Also consider metrics of movement quality, not just performance parameters.
The LSI value calculated by the ReGo system does not only include the main outcome parameter. In the case of the Balance Front Hop Test, the following metrics are included in the LSI value:
- Sway Area
- Longitudinal Balance Point
- Transversal Balance Point
- Time to Stabilization
Third, it is important to have baseline values from before the injury, as the LSI score might overestimate hopping performance due to deficits in knee function in both the uninjured and injured leg following ACL reconstruction (14-16). If pre-injury data is not available, a practical approach would be to perform the tests with the contralateral limb before surgery (12). This would shift the rehabilitation focus to not just matching LSI but also restoring the contralateral limb’s performance before injury or surgery.
In summary, when implementing hop testing, it’s important to use a test battery rather than a single test, incorporating various planes of movement for a comprehensive assessment of knee function. Additionally, the LSI value should not be the sole metric for RTS decisions; include other movement quality measures and use pre-injury or pre-surgery baseline data to guide rehabilitation.
Comments on Measurement Equipment
Most often, hop tests like the front hop are qualitatively evaluated by an expert.
Conversely, the introduction of the ReGo sensor insoles to hop testing represents a major advancement for trainers and therapists. The sensor insoles offer an affordable, valid, and reliable tool for gaining in-depth insights into the biomechanics of jumping and landing. They measure key factors related to landing quality, such as the Balance Point and Sway Area and the Time to Stabilization. This allows for a detailed analysis of an athlete’s performance beyond subjective evaluation.
The following table (Tab-1) contains product specifications, outlining how trainers and therapists benefit from the sports performance and functional tests.
| Funktion | Beschreibung |
| 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. |
In summary, the ReGo system helps trainers and therapists by delivering objective biomechanical hop testing outcomes, making it an essential tool for informed decision-making in the RTS process.
Literaturverzeichnis
- Larwa, J., Stoy, C., Chafetz, R.S., Boniello, M., Franklin, C. (2021). Stiff Landings, Core Stability, and Dynamic Knee Valgus: A Systematic Review on Documented Anterior Cruciate Ligament Ruptures in Male and Female Athletes. International Journal of Environmental Research and Public Health. 18(7), 3826.
- 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.
- Mohammadi, F., Salavati, M., Akhbari, B., Mazaheri, M., Khorrami, M., Negahban, H. (2012). Static and dynamic postural control in competitive athletes after anterior cruciate ligament reconstruction and controls. Knee Surg Sports Traumatol Arthrosc, 20(8), 1603-10.
- Heinert, B., Willett, K., Kernozek, TW. (2018). INFLUENCE OF ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION ON DYNAMIC POSTURAL CONTROL. Int J Sports Phys Ther, 13(3), 432-440.
- A Zouita, B. M., Zouita, S., Dziri, C., Ben Salah, F. Z. (2009). Single-leg assessment of postural stability and knee functional outcome two years after anterior cruciate ligament reconstruction. Ann Phys Rehabil Med, 52(6), 475-84.
- Webster, K. A., Gribble, P. A. (2010). Time to Stabilization of Anterior Cruciate Ligament–Reconstructed Versus Healthy Knees in National Collegiate Athletic Association Division I Female Athletes. J Athl Train, 45 (6), 580–585.
- DuPrey, K. M., Liu, K., Cronholm, P. F., et al. (2016). Baseline Time to Stabilization Identifies Anterior Cruciate Ligament Rupture Risk in Collegiate Athletes. The American Journal of Sports Medicine, 44(6),1487-1491.
- 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.
- Welling W., Benjaminse A., Seil R., Lemmink K., Gokeler A. (2018). Altered movement during single leg hop test after ACL reconstruction: implications to incorporate 2-D video movement analysis for hop tests. Knee Surg Sports Traumatol Arthrosc, 26(10), 3012-3019.
- 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.
