| The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments, with over 250,000 injuries per year in the United States. Its primary function is to limit anterior tibial translation when the quadriceps muscle group contracts to extend the knee. Previous studies have found that ACL-deficient individuals avoid use of the quadriceps in the injured limb as a means of limiting anterior movement of the tibia in the absence of a functioning ACL. This altered gait pattern has been found to persist in the period following ACL reconstruction surgery, and inhibits the ability of patients to return to full quadriceps strength during physical therapy. A study by Hunt et al. investigated the existence of quadriceps avoidance in stationary, isokinetic cycling, a common rehabilitation exercise, and found that the injured individuals not only practiced avoidance of the quadriceps, but avoidance of the entire limb as well. This is possible because a large increase in output from one limb can effectively maintain the necessary cadence required in isokinetic cycling. From these results, a study was designed to investigate the effectiveness of isokinetic single-leg cycling in increasing quadriceps strength. Ten control and seven ACL-reconstructed subjects participated in an IRB approved study that consisted of a series of 15 second cycling trails in isokinetic mode at 75 rpm, while kinematic, kinetic, and electromyographic data of the lower limbs were collected, with the trials including both double-leg cycling and single-leg cycling. It was hypothesized that there would be an increase in quadriceps muscle activity, peak knee extensor moment, and knee joint power in single-leg cycling when compared to double-leg cycling. Results of the study, although not statistically significant (p<0.05), hinted at the possible effectiveness of isokinetic single-leg cycling in increasing quadriceps use. A trend in data demonstrated that given a specific limb power, more quadriceps muscle force would be generated in the single-leg task when compared to the double-leg task. Future studies should investigate the muscle activation patterns associated with single-leg cycling, and should involve a testing protocol that assesses the performance of ACL reconstructed individuals at multiple time points in physical therapy. |
