the voluntary response index in electromyographic study during landing test of the patients with acl deficiency: a new study protocol

background: daily increased rate of anterior cruciate ligament (acl) injuries in athletes calls for more investigation in these patients to differentiate copers from noncoper acl-deficient (acld) knees as soon as possible. objectives: the current study aims to introduce a new electromyographic protocol, named voluntary response index (vri), that might help to categorize and differentiate patients with acld knee from others in the early stage. materials and methods: thirty-four patients with acld knee were allocated into two equal groups, namely, coper and noncoper groups, based upon their ability to return to sport during the preceding six months. the patients with acld knee were asked to perform a jump on a force platform from a 75-cm distance. results: the results were compared with 17 matched healthy participants. the electromyographic disposable electrodes were attached to the seven muscles of the lower extremity of the participants before performing the test. the outcome measures were the magnitude and similarity index of the vri, time to stop, vertical ground reaction force, the displacement of the center of pressure’s (cop) path line length, and the participants’ tegner, ikdc (international knee documentation committee) as well as koos (knee injury and osteoarthritis outcome score) questionnaires scores. using the appropriate statistical analysis, the electromyographic and force plate data were compared among the three groups. all efforts went into determining whether an association exists between the findings of each group and the participants’ functional questionnaires scores. conclusions: the results of this study would be helpful in objectively differentiating the patients with acld knee into coper and noncoper groups to receive appropriate treatments before their return to the competitions.