Part 1: Return to Sport after ACL injury: Are Traditional Hop Tests Enough?

Be it an ACL tear or ankle sprain, hop tests are a commonly used return to sport (RTS) test used in the clinic. While these hop tests are a valuable tool, they do not give us the entire picture of an athlete’s readiness to get back to their sport. At our ACL Performance Lab, we use a comprehensive battery of objective tests to determine when our athletes are ready to get back in the game.

A 2021 study analyzing the many components of ACL rehab emphasized, “It should be noted that hop tests are a valid measure of a patient’s ability to perform a hopping task rather than assessing any specific physical quality. Because of this, a critical examination of single leg hop tests showed that clinicians tend to overestimate lower extremity function when using hop distance alone” (Larson et. al 2021). So what are the hop tests and how should we utilize them? Let’s find out. 

What are the hop tests?

Traditional hop tests were first seen in the literature in the 1980s-1990s as an evaluative tool to measure progress and return to sport (RTS) readiness following an ACL injury.  A great visual of the 4 traditional hop tests can be found here. 

Davies et. al noted in his recent review of the hop tests that, “These studies were among the first to objectively assess functional performance as part of a criteria driven RTS process” (Davies et. al 2020). But how functional are these test? Does an athlete’s ability to hop on one leg translate to their ability to play their sport? Functionality is highly specific to the task at hand: the functionality required on the lacrosse field is different than the functionality required on the basketball court. So how can 1 test predict every athlete’s readiness? 

What are hop tests good for? 

While the hop tests may not be perfect, they do have some value. Physical therapist, Dr. Wesley Wang notes, “I utilize the hop tests to assess the power of the lower extremities, the athlete’s confidence and neuromuscular control”(Wang),  all vital components that must be cleared before returning the athlete to their sport.

The hop tests are valuable for a few reasons: they’re easy to perform in a clinic, they measure side to side differences, and they can begin to assess an athlete’s change of direction abilities and power production. 

A “passing” score on the hop test is defined by getting a score >90% on the LSI, or limb symmetry index. This means that if the non-injured side scored a 100, the injured side scored a 90. 

Are hop tests enough? 

One major downside of the traditional horizontal hop tests used as an ACL return to sport parameter is that these tests only measure distance. This leaves many other factors out of the picture like take off and landing strategies, trunk control, and other compensatory mechanisms an athlete may adopt to jump as far as possible.  Measuring quantity (how far an athlete can jump) does not take into account the quality of their jumping ability. In essence, it doesn’t really matter how far you can jump or how symmetrical your jumping abilities are if the quality of movement is lacking. 

Physical therapist, Dr. Pollen, writes, “Remember, athletes are master compensators. When a challenge is put in front of them, they can often find a way to reach the target while working around any physical deficiencies they might still have. During a hop test, an athlete can make up for a lack of quadriceps power by generating extra power at the hip and/or ankle” (Physio Network). 

Another downside of the traditional hop tests is that they strictly assess symmetry, or side to side differences. This is the 90% LSI score mentioned above. A recent study looked at 126 athletes and found that at their time of return to sport when only looking at the  hop tests, every single athlete displayed some sort of asymmetry. What does this tell us? Perhaps this means these athletes weren’t ready to go back on the field. Or perhaps it meant that every human is going to have some side to side asymmetries We can’t know for sure. But it does tell us that symmetry is not the end all be all as an evaluative tool for risk of injury or return to sport. Most healthy people will have some asymmetries! Another interesting and not surprising point: many athletes display weakness in the uninjured limb post surgery, strictly from underuse. Thus, comparing the injured side to this uninjured, but now deconditioned side, may not give us a valid measurement of this person’s true potential. Sure, it may be “symmetrical,” comparatively, but this will not represent the true strength and power that athlete holds.

Lastly, how relevant are jump tests to an athlete’s ability to cut on the lacrosse field, go up for a layup, or come down from a header? The hop tests fall short in their physical resemblance of athletic movements and in their environmental context. Most tasks required in sport neccesitate multitasking. With the hop test, the athlete is able to focus solely on the task of jumping without distraction. This is valuable in the beginning stages of rehab when there may be fear surrounding jumping. However, when it is time to get back on the field, the hop tests don’t do a great job of mimicking what a “game time” scenario would look like. 

Let’s Get Vertical! 

As the literature started to show these downfalls, researchers set out to find other reliable measurement tools for ACL return to sport protocols. One promising test the literature found has been the vertical jump, vertical depth jump, and 10 second vertical jump.  

A study looked at 126 athletes who were cleared to return to sport using traditional return to sport tests like the horizontal hop. However, when these same athletes were tested on vertical drop and vertical jump, they all displayed deficits in concentric power compared to their unaffected side, as well as compared to their non-injured controls (Kotsifaki et. al 2022). 

Concentric power is the “explosive” part of a jump, after you have loaded, where you are now starting to get truly vertical. These athletes “achieved 97% symmetry in the horizontal performance (hop distance) but only 83% and 77% symmetry in the vertical performance (jump height) of the single vertical jump and the single leg drop jump, respectively” (Kotsifaki et. al 2022).

Another test analyzed force-time abilities as a predictive measure of ACL injury. Researchers asked the question: Does an athlete’s ability to produce force correlate with their risk of future ACL injury? After testing D1 athletes using force plates and following them throughout their seasons, researchers did find an association between athletes explosive abilities and later ACL injury (Pontillo et. al 2021). 

This just tells us that the traditional horizontal hop tests don’t give us the full picture. While they can be a useful piece of the puzzle, they leave some important measures unmet. Additionally, just because vertical jump tests tell us more about an athlete’s explosive abilities, it STILL doesn’t give us the whole picture. Pontillo and researchers noted that while utilizing force plates is a reliable tool, we still have to consider other factors such as “lower extremity proprioception, dynamic balance, hamstring strength, hamstring: quadriceps force ratio and raising awareness of potential injury” in assessing an athlete’s ACL injury risk and return to sport readiness (Pontillo et. al 2021).  

Can the hop tests be used as a part of the rehab protocol? Of course, but it should not be the only test used. Interested in working with one of our Made 2 Move physical therapists or athletic trainers in your transition back to the field, gym, court, or life? Book a free consult here to start your journey back to playing sports confidently anf safely. And tune into next week’s blog for a detailed description of what a comprehensive RTS protocol should look like!