Study Design Cross-sectional, controlled laboratory study. Background Quantification of muscular activation during different phases of functional activities is important to understand activation deficits in individuals who have undergone anterior cruciate ligament reconstruction (ACLR). Objectives To compare activation levels of the vastus medialis (VM), medial hamstrings (MH), and gluteus medius (GMed) muscles during the different phases of weight-bearing tasks between individuals who had undergone ACLR and healthy controls. Methods Surface electromyography was used to measure the activation levels of the VM, MH, and GMed muscles in 16 participants who had undergone ACLR (average time since surgery, 4 years) and 15 healthy participants during the reach and return phases of the Star Excursion Balance Test (SEBT) and the ascending and descending phases of a step-down task (SDT). Repeated-measures analyses of variance were performed to determine whether muscle activation levels differed between groups during different phases of the tasks. Results There were significant group-by-phase interactions for the GMed during both the SEBT and SDT. Gluteus medius activation was lower for the ACLR group during the return phase of the posteromedial direction of the SEBT compared to the control group (P = .03). During the SDT, GMed activation was higher for the ACLR group during the ascending phase than during the descending phase (P<.001), while the control group showed no difference between phases (P = .71). Conclusion Individuals who had undergone ACLR have similar VM and MH activation compared to healthy individuals during different phases of the SDT and SEBT. However, phase differences for GMed activity and decreased GMed activity relative to healthy individuals were observed among ACLR participants. J Orthop Sports Phys Ther 2016;46(11):984-992. Epub 11 Oct 2016. doi:10.2519/jospt.2016.5896.
Keywords: Star Excursion Balance Test; anterior cruciate ligament; electromyography; gluteus medius; knee joint.