Following ACL reconstruction, most practitioners determine when an athlete should return to sport by measuring horizontal distance during various hop tests. Hop tests have been widely adopted by the rehab community, mostly because they are easy to perform and do not need expensive equipment. Unfortunately, these tests are unable to predict successful return to sport one year following injury causing some experts to question their validity as a return to sport metric.
This study confirms that rather than evaluating hop distance, a more sensitive barometer for return to sport following ACL reconstruction is single leg vertical jump performance. These tests are easy to administer, with the simplest being the single-leg jump test (SLJ). To perform this test, have the athlete stand on one leg, drop to a self-selected depth and then jump vertically with maximum effort and land on the same leg. Vertical height distance can be compared bilaterally. An alternate way to perform this test is with the single-leg drop jump (SLDJ). The test is performed by having the athlete drop off of a 15 -cm step and jump vertically, landing on the same leg.
The authors of this study show that previously injured athletes who had been cleared for return to sport using the hop distance protocols had significant impairments in single-leg jump performance. Specifically, even though athletes following ACL reconstruction achieved 97% symmetry in horizontal hop distance, only 83% and 77% symmetric in the single-leg vertical jump and single-leg drop jump test, respectively. Importantly, the authors also performed EMG analysis of every muscle in the hip, knee, and leg as athletes performed the jump tests and concluded that weakness of the soleus muscle was the single best predictor of poor performance. This fits with prior research showing that because soleus prevents anterior translation of the tibia, it is a powerful stabilizer of the anterior cruciate ligament. In fact, research from Australia shows that because soleus limits anterior translation of the tibia, it provides greater protection to the anterior cruciate ligament than all of the hamstrings combined. (For more information, go to the article section of this site and read The Overlooked and Underappreciated Soleus.)
My favorite way to strengthen the soleus is with bent-knee heel raises using the ToePro. The lateral tilt to the ToePro allows you to move the heel from full inversion to eversion while performing heel elevations. Moving to a full range of motion is necessary to access all fibers of the soleus muscle. It also allows you to strengthen synergists to the soleus, such as flexor hallucis longus, which was not evaluated in this study and may play a key role in achieving maximum vertical jump height.