Injuries to the anterior cruciate ligament (ACL) are among the most severe a competitive athlete can face. The ACL is crucial in maintaining both stability and functionality of the knee joint. Each year, between 100,000 and 200,000 athletes of all levels in the United States suffer an ACL tear, frequently sidelining them for up to a year of intense rehabilitation.

A new study from Yale Sports Medicine published in the Journal of Strength and Conditioning Research reveals that a quick vertical jump test using force plate technology could provide a powerful shortcut to identify at-risk athletes before an injury occurs.

For those who do undergo ACL reconstruction, the force plate technology, which has been increasingly more available in athletic training departments, physical therapy offices, and is now even at some Yale sports medicine clinics, can be used to improve clinical guidance during recovery and impact return-to-sport decisions.

Injury risk screenings

The best way to treat an ACL injury is to prevent it from occurring in the first place. To spot athletes who move in ways that jeopardize their joints, sports medicine scientists rely on two primary evaluation tools: the landing error scoring system and the Y-balance test.

The landing error scoring system evaluates how an athlete absorbs impact. An athlete jumps off a 30-centimeter box, lands, and immediately rebounds into a vertical leap. A medical professional reviews the recorded video footage to score nine specific movement errors, such as whether the knees collapse dangerously inward upon contact.

Meanwhile, the Y-balance test measures dynamic balance and physical symmetry. While standing on a single leg, the athlete reaches their opposite foot as far as possible in three distinct directions. If the maximum reach distance between the left and right legs differs by more than 4 centimeters, it signals a significant muscle imbalance. This imbalance makes the athlete two and a half times more likely to sustain an injury.

While both traditional screenings are highly studied, they require substantial time, dedicated physical space, and expert staff to record and interpret. For a sports program without access to this expertise, performing these evaluations on each competitor when there are hundreds of student athletes can be extremely challenging.

Rapid, high-tech screenings

Seeking a faster and simpler alternative, the Yale research team investigated the countermovement jump, a simple jump skill which is currently used in many elite training centers to monitor the power and fatigue of an athlete.

This test requires an athlete to stand on a portable dual force plate, which is like an advanced electronic scale that measures forces applied by the body. The athlete places their hands on their hips to isolate the lower body, squats rapidly, and jumps as high and fast as possible.

Within seconds, the force plates record thousands of data points per second. The technology maps exactly how much power the athlete produces, how symmetrical their legs are during movement, and how they handle the impact of landing. Because specialized software automates the entire data analysis process, a whole team can be screened in a fraction of the time required by traditional methods, without requiring advanced clinical expertise to run the test.

To determine if this rapid test could mirror the insights of older assessments, researchers recruited more than 100 NCAA Division I athletes from the Yale football, women's soccer, and women's lacrosse teams, all sports with notoriously high rates of ACL injuries. During off-season training, the athletes completed the force plate jump alongside both traditional screenings to compare results.

What force plate data showed

The study’s findings revealed a direct bridge between an athlete's performance on tedious movement tests and the automated data captured during a single vertical jump.

Athletes who scored poorly on the video-based landing assessments exhibited significantly higher landing stiffness on the force plates. Landing stiffness describes an athlete’s inability to smoothly absorb impact through their muscles, which forces the shock of landing to travel directly into their bones and joints.

"Stiff landings mean the body isn't using its natural shock absorbers like the hamstrings, glutes, and quadriceps, to safely dissipate energy," explains Liz Gardner, MD, an associate professor of orthopedic sports medicine, head team physician for Yale Athletics, and principal investigator for the study. "When an athlete lands hard instead of bending softly through the hips and knees, that impact force is transferred directly to the knee joint, placing the ACL under dangerous levels of stress."

The researchers also tracked an experimental “at-risk flag count," assigning a point for every high-risk threshold an athlete crossed across the traditional tests. They discovered a compounding effect: the more movement flags an athlete accumulated, the more chaotic and asymmetrical their force plate jump data became.

Improving return-to-sport decisions

The utility of force plate technology extends far beyond initial injury prevention. When an ACL tear does occur, determining exactly when an athlete is truly ready to return to high-level competition is a notoriously difficult decision for surgeons and physical therapists.

Gardner and her team are expanding the use of force plates directly into the surgeon's office to guide these critical clinical decisions. Standard follow-up appointments are often limited to basic assessments like joint range of motion, manual muscle testing, or observing simple hops and squats. Unfortunately, these basic movements do not accurately mimic the intense, chaotic stressors that competitive sports place on a recovering knee.

By utilizing the countermovement jump in an office setting, doctors can gather objective, immediate feedback on whether an athlete's surgically repaired knee has recovered the necessary strength and symmetry to safely handle the demands of their sport. This data helps eliminate the subjective guesswork from clearance decisions, reducing the risk of re-injury.

While force plate jump testing is not intended to completely replace hands-on clinical exams, it serves as an invaluable, objective screening tool to sort large groups of athletes efficiently. By tracking vertical jumps routinely, coaches, athletic trainers, and physicians can instantly flag athletes who are landing too stiffly or pushing unevenly, funneling them into targeted physical therapy long before injury strikes.

(Newswise/HG)