Determining the Effects of Non-invasive Brain Stimulation to Improve Quadriceps Muscle Function After ACL Reconstruction.

Quadricep muscle impairments persist for years after anterior cruciate ligament reconstruction (ACLR). Recent evidence suggests that lower neural drive, (i.e., lower corticospinal excitably (CSE)), is associated with pronounced quadriceps muscle performance deficits, which are more severe in females recovering from ACLR than in males. Current postoperative rehabilitation protocols do not target lower neural drive, which can be achieved through non-invasive brain stimulation. Thus, the long-term goal of this research is to improve the effectiveness of ACLR rehabilitation. The objective of this project is to determine if neural drive is the critical missing link in ACLR rehabilitation. To meet this objective, the investigators will administer anodal transcranial direct current stimulation (tDCS), a type of non-invasive brain stimulation known to increase CSE. The investigators will then assess whether it improves three measures of quadriceps muscle performance (in Aim 1) and two measures of CSE (in Aim 2). In Aim 3, the investigators will determine the relationship between observed changes in quadriceps muscle performance and CSE in female participants recovering from ACLR. These aims will be achieved using a randomized, triple-blinded clinical trial with 42 female individuals after ACLR between the ages of 18 and 35 years. All participants will receive six sessions of active or sham anodal tDCS while they perform isolated quadriceps exercises on an isokinetic dynamometer. The two measures of CSE (i.e. active motor threshold and the slope of transcranial magnetic stimulation (TMS) induced recruitment curves) will be determined using surface electromyography on the vastus medialis and TMS. Three measures of quadriceps performance (i.e. peak torque normalized to body weight, rate of torque development (RTD) from 0-100ms and 100-200ms, and torque steadiness) will be determined following standard isometric muscle testing on an isokinetic dynamometer with the hips flexed to 90° and the knees flexed to 60°.