Relevance for the sport
Many sports, such as basketball, soccer, and tennis, require athletes to perform dynamic maneuvers like cutting and landing. Poor biomechanics during these actions increase the risk of injuries, particularly to the knee and ankle (1–2). The side hop test offers a standardized method to assess lower limb function, focusing on the ability to generate force and maintain balance during lateral movements. This makes it especially relevant for sports involving frequent cutting and landing actions (3).
In rehabilitation, the side hop test is widely used to monitor recovery from lower limb injuries, such as anterior cruciate ligament (ACL) tears or ankle sprains. Clinicians rely on it to evaluate functional improvements and determine an athlete’s readiness to return to sport (RTS). By using unilateral tests like the side hop, side-by-side performance comparisons can be made through the Limb Symmetry Index (LSI). An LSI score above 90% is considered the benchmark for healthy individuals and those completing rehabilitation (4–6).
Information
The LSI is defined as = (injured limb value / uninjured limb value)*100.
However, despite achieving high LSI scores, some athletes may still exhibit poor landing biomechanics, which increases the risk of re-injury (3, 9–10). Research suggests that movement quality during hop tests is an independent factor that often does not align with performance metrics like hop distance or symmetry (2, 9, 11). This underscores the need to evaluate movement quality separately from functional performance to ensure a safer RTS for athletes (10).
Test Protocol
The ReGo Balance Side Hop is a single-legged hop test performed sideways and back over a 40 cm distance on a flat surface (Fig-1). The primary objective is to execute the hops with proper landing mechanics and maintain balance for three seconds after each landing, both when hopping sideways and back.
Each leg is tested three times, with the average of all valid repetitions being evaluated. Proper form requires the hands to rest on the hips, the hips to remain level, and the knee to stay behind the toes upon landing.
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A trial is considered invalid if
o the landing occurs inside the 40 cm mark,
o balance is not maintained during the holding phase, or
o the free foot touches the ground
Outcome Parameters
The ReGo Balance Side Hop test evaluates the quality of landing mechanics during lateral and medial hops. Thus, the primary outcome parameter of the Balance Side Hop is Balance Point & Sway Area (Fig-2).
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The primary outcome parameter of the ReGo Balance Side Hop is Balance Point & Sway Area.
The Balance Point represents the average position of the center of pressure (COP) of the landing foot during the balance phase. This phase begins 0.5 seconds after the foot makes initial contact and lasts for 3.0 seconds. The Balance Point reflects how the load is distributed across the foot, indicating whether weight is shifted toward the forefoot, hindfoot, medially (inward), or laterally (outward).
The Sway Area represents the size of an ellipse that contains 95% of the COP data points during the balance phase. This measurement reflects the stability of the foot’s contact with the ground over the 3.0-second balance phase, with a smaller Sway Area indicating better stability and control.
Both the Balance Point and Sway Area are presented as numerical values, along with a percentage indicating the left/right (L/R) difference.
Information
The Longitudinal and Transversal Balance Points are normalized by sensor insole length and width providing a standardized way to describe load distribution across the foot:
o The hindfoot and lateral side start with 0
o The forefoot and medial side end with 1
In this example, the Sway Area on the left side is nearly 20% larger than the right, indicating reduced landing stability on the left. The Balance Point is located further forward and slightly more laterally on the left side compared to the right.
Understanding how metrics like Balance Point and Sway Area relate to dynamic postural stability is crucial, particularly in athletes recovering from ACL injuries. Research indicates that postural stability during a single-leg stance is often compromised in the affected leg following ACL injuries, other knee injuries, or ACL reconstruction (ACLR) when compared to the non-injured leg or healthy controls (12–14). For example, individuals with a knee injury sustained 3–10 years earlier demonstrated greater medio-lateral sway during a single-leg stance and reduced single-leg hop performance (12). However, Zouita et al. (14) reported no differences in single-leg hop performance despite observing impairments in postural stability during a single-leg stance in ACL-reconstructed individuals.
But do injured individuals also show differences in postural stability during landing tasks? Athletes returning to sport after ACLR exhibit significant deficits in dynamic postural stability (15) and greater COP excursion (16) in the reconstructed limb compared to the non-surgical limb during single-leg landing and hopping activities.
Conversely, some studies have found no significant differences in dynamic postural stability between ACL-reconstructed athletes and matched controls or between their involved and uninvolved limbs shortly after being cleared for sport (17), highlighting variability in outcomes depending on the timing and measures used for assessment. Ultimately, further research is needed to establish a clear connection between specific qualitative aspects of hop tests and their potential to discriminate between injured and uninjured athletes, with the goal of supporting better-informed RTS decisions.
In addition to Balance Point and Sway Area, Time to Stabilization (TTS) and Stabilization Progression offer deeper insights into dynamic postural stability (Fig-3). These metrics capture the temporal and progressive aspects of stabilization, providing a clearer picture of how quickly and effectively an athlete regains balance after landing.
TTS measures the time it takes for the COP velocity to decrease below a predefined stabilization threshold. Stabilization Progression visualizes the COP’s traveling velocity over time, depicted as horizontal bars from the moment of landing (bottom) to the end of the balance phase (top). Here, TTS on the left is 30% higher than on the right, qualitatively supported by greater deflections in the Stabilization Progression.
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Time to Stabilization and Stabilization Progression provide additional measures of dynamic stability, highlighting recovery or potential risk factors.
These metrics are particularly useful for identifying subtle asymmetries that might not be apparent through observational assessments. Current literature indicates that athletes who have undergone ACLR experience increased TTS after jump landings (18). Furthermore, higher TTS during jump landings is associated with a greater risk of ACL rupture (19).
In summary, the ReGo Balance Side Hop test provides critical insights into postural stability, which can inform RTS decisions and injury prevention strategies. Further research is essential to enhance our understanding of how landing mechanics correlate with injury risks and recovery.
Example
Let’s look at a real data example. In Vid-1, you see a young professional athlete (U17) from a club in Germany’s 3rd soccer league who suffered an ACL tear in his right knee approximately 14 months before the test was conducted.
On the left side (displayed on the left in Vid-1), the athlete compensates with his upper body during both lateral and medial jumps to maintain balance after landing. However, the knee appears stable during these movements. Upper-body compensation is also evident during jumps on the right side to stabilize landings. However, the knee appears stable here as well (e.g., no knee valgus).
Let’s examine the objective outcome parameters of the ReGo Balance Side Hop. Fig-4 shows that the Balance Point is further forward on the left side and more laterally oriented than on the right. These metrics differ by approximately 10% between the two sides. Baseline values from before the injury would be highly valuable for classifying these results. The Sway Area on the right side is significantly larger—by nearly 60%. This indicates that the ACL injury continues to affect landing stability, even if it is less visually apparent.
The qualitative analysis of the Stabilization Progression (Fig-5) confirms greater instability on the right side. Additionally, the Time to Stabilization is approximately 6% longer on the right.
The LSI score for this test is 85%, reflecting asymmetries in landing mechanics. Note that calculating the LSI score for the ReGo Balance Side Hop incorporates multiple outcome parameters.
Information
The LSI score of the ReGo Balance Side Hop takes the following outcome parameters into account:
o Sway Area
o Longitudinal Balance Point
o Transversal Balance Point
o Time to Stabilization
In summary, the data indicates that landing stability on the right side remains impaired due to the ACL injury sustained 14 months ago, potentially increasing the risk of knee reinjury (20). Evidence suggests that delaying RTS by each additional month, up to nine months post-ACLR, reduces the risk of reinjury by approximately 50% (21). Unfortunately, no data is available on when this athlete was cleared for sports after his ACL injury.
This example demonstrates how the outcomes of the ReGo Balance Side Hop test offer valuable insights into landing mechanics and quality, providing trainers and therapists with objective data to guide RTS decisions.
Tips for Trainers and Therapists
Preventing ACL injuries requires an evidence-based approach, combining research insights with practical application. This chapter explores current evidence on reducing ACL injury risks, offering trainers and therapists actionable strategies. While there isn’t one definitive superior program to reduce ACL injury risk, multifaceted approaches incorporating various exercise types appear to be the most beneficial (22). Here are some specific interventions that have shown promising results:
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Include multiple interventions, such as technique training, plyometrics, and warm-up routines, to help lower the risk of ACL injuries.
Technique Training: Provide athletes with clear instructions and feedback on proper landing technique. Focus on achieving a soft landing with adequate knee flexion. This can be implemented with minimal training setup and does not require specialized coach education (22–23).
Plyometrics: Incorporate plyometric exercises into training routines. These exercises help develop strength and power, which can improve landing mechanics and contribute to safer movement patterns. This could involve exercises such as hurdle jumps, squat jumps or box jumps, for instance. See Tab-1 for detailed instructions and volume recommendations for the squat jump. Consider gradually increasing the intensity of plyometrics to avoid overloading athletes (22–23).
| Category | Name | Procedure |
|---|---|---|
| Jumps | Squat Jump | o Begin in an upright position, feet shoulder-width apart o Hold hands on hips o Bend the knees to get into a half-squat position o Immediately reverse the downward movement and jump up as high as possible o Extend the hips, knees, and ankles, land in the same position as takeoff o First, stick the landing, reset and start the next repetition o Progress to performing multiple repetitions without a break in between |
| Volume | Recommendation | o 4 sets with 4-6 repetitions per session o Rest between sets: 30 – 90 seconds |
Warm-up Programs: Integrating a comprehensive warm-up program that encompasses technique training, plyometric, and balance exercises has been identified as a beneficial strategy for injury prevention. By addressing multiple risk factors concurrently, these programs offer a holistic approach to mitigating ACL injury risks (23).
Information
Training interventions to reduce ACL injury risk should begin in the pre-season and continue into the season.
Although there is no definitive guideline regarding the ideal duration and frequency of ACL interventions available in the scientific literature, the general consensus is to initiate these programs during the pre-season and maintain them throughout the season (22).
It is crucial to emphasize that the optimal training program may vary depending on factors such as the specific sport, the athlete’s individual characteristics, and the level of competition. A well-rounded approach that addresses multiple risk factors through a combination of technique training, plyometric exercises, and warm-up programs is recommended to reduce ACL injury risk (22).
Comments on Measurement Equipment
Hop tests, such as the side hop, are often assessed qualitatively by experts.
In contrast, the ReGo Sensor Insoles represent a notable advancement in hop and jump testing for trainers and therapists. They offer an accessible, valid, and reliable method for obtaining detailed insights into jumping and landing biomechanics. The Sensor Insoles capture key metrics, including jump-off force, impulse, timing, and landing quality indicators like COP variability.
This technology facilitates an in-depth analysis of an athlete’s performance, highlighting specific areas for targeted training interventions.
The following table (Tab-2) outlines the product specifications, providing essential details for improving sports performance and conducting functional assessments.
| 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. |
Im Wesentlichen unterstützt das ReGo-System Trainer und Therapeuten, indem es einen verbesserten Zugang zu biomechanischen Metriken für Hopfentests bietet, was es zu einem wertvollen Werkzeug für fundierte Entscheidungen macht.
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