Single-leg hop can result in higher limb symmetry index than isokinetic strength and single-leg vertical jump following anterior cruciate ligament reconstruction.

Background: A single-leg vertical jump height (SLVJ) may reflect knee extension strength more than a single-leg hop for distance (SLH). This study aimed to examine the relationships between the isokinetic knee extension torque, SLH, and SLVJ after anterior cruciate ligament reconstruction (ACLR).
Methods: Forty-four patients post-ACLR (median 12.0 months) participated in the study. The isokinetic knee extension peak torque at 60°/s and 180°/s (Ext 60, 180), SLH, and SLVJ were measured. The limb symmetry index (LSI) was calculated as the ratio of the operated side to the unoperated side.
Results: There were moderate-to-strong positive correlations between isokinetic knee extension torque and both SLH (r = 0.72-0.77, P < 0.001) and SLVJ (r = 0.73-0.79, P < 0.001). Significant side-to-side differences in isokinetic knee extension torque and SLVJ between the operated and unoperated sides were found (P < 0.05), but not for SLH (P = 0.065). The results of the analysis of variance (ANOVA) and post hoc analyses showed that the LSI of SLH (98.2%) was higher than that of the LSI of Ext 180 and SLVJ (P < 0.05). Fisher's exact test showed a significant relationship between the LSI of Ext 180 and that of SLVJ (cut-off 85%; P = 0.041). No patients had LSI < 85% in SLH.
Conclusions: Even though SLH asymmetry improved approximately 12 months after ACLR, the asymmetry of isokinetic knee extension torque and SLVJ remained. The LSI of SLVJ could be an indicator of the recovery of isokinetic knee extension torque.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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