People might not frequently hop backward, but recent research indicates that hopping backward on one leg could be an effective way to assess strength and recovery in the knee, along with other joints and muscles in the leg after ACL reconstruction surgery. Additionally, this method is simpler to implement and requires minimal specialized tools for healthcare providers such as physical therapists.
Progress sometimes requires taking a step back.
In the context of patients healing from ACL reconstruction, jumping backward may serve as a useful indicator of their readiness to return to sports.
A researcher from the University of Kansas is spearheading studies that explore how single-leg backward hopping can aid in assessing the recovery journey of individuals who have undergone anterior cruciate ligament reconstruction. Preliminary findings suggest that the distance achieved during backward hops provides insight to practitioners, therapists, and researchers regarding the strength, force, and recovery of the knee.
Though backward hopping might not seem like a typical activity, current research suggests it is a valid method for evaluating knee function and quadriceps strength. Unlike some standard assessments such as vertical jumps, it necessitates little more than a flat surface and a tape measure.
“The objective is to provide practitioners with an accessible way to gauge a person’s status after an ACL injury and throughout their recovery process,” stated Yu Song, assistant professor of health, sport & exercise sciences at KU, who is the study’s lead author. “Typically, recovery is measured by forward hopping distance, but studies have indicated that this can obscure the true condition of knee recovery. We aim to achieve a more nuanced evaluation with precise metrics.”
In the study, researchers enlisted participants without ACL injuries to establish the feasibility of using backward hopping for assessing knee function and quadriceps strength deficits. Participants performed single-leg backward hops before and after fatiguing their quadriceps through unilateral exercise. While hopping, they stood on a force plate, a device that measures the amount of force exerted.
Biomechanical measurements of the hip, knee, and ankle were taken during all three movements. The knee mechanics showed a significant decline after the fatigued leg was exercised. The backward hopping distances exhibited the most notable decrease, with participants capable of only about 84% of their pre-fatigue force and distance. In contrast, they managed to perform at over 90% of their pre-fatigue metrics in other hopping movements.
“The knee’s contribution is relatively minor, particularly when compared to the hip in forward jumps,” noted Song. “However, this is different in backward hopping, where knee engagement is significantly greater—about twice as much—during that movement.”
The single-leg backward hopping demonstrated the highest peak knee torque, peak knee power, and knee work compared to forward and vertical hopping. These findings suggest that backward hopping may function as an equal or superior method for assessing quadriceps strength deficits in those recovering from ACL surgery, according to Song.
This study, co-authored by Boyi Dai from the University of Vermont, along with Lauren Salsgiver, Kaden Van Valkenburg, Natalie Christofferson, Yessica Lo, Zhichen Feng, and Brenna McGuinness, all from the University of Wyoming, was published in the Journal of Sport and Health Science.
The results merit additional exploration with individuals convalescing from ACL reconstruction. Song, alongside Ashley Herda, an assistant professor and the director of KU’s Exercise and Human Performance Laboratory, and collaborators at the KU Medical Center are commencing efforts to recruit patients currently undergoing rehabilitation for inclusion in further studies. This research could help substantiate single-leg backward hopping as a reliable measure of recovery status, ultimately fostering a partnership between patients and medical professionals to ensure improved recovery outcomes and a faster, safer return to athletic activities.
Although hopping backward on one leg may not seem intuitive, it could potentially unlock a pathway to advancement.
“While many may not associate knee function or backward hopping with natural movement, individuals often utilize backward motion, like walking backward, during rehabilitation,” Song explained. “We aim to deepen our understanding of single-leg hopping and have found it to be a significant and accurate indicator of knee strength.”
