The Effects of Backwards Walking on Quadriceps Muscle Activation after ACL Reconstruction: A Pilot Study

Quadriceps muscle activation is commonly decreased in persons after ACL reconstruction. Backwards walking has been studied as an intervention to improve quadriceps muscle strength for individuals with knee osteoarthritis. However, it is unknown if backwards walking could increase quadriceps muscle activation in persons with anterior cruciate ligament injuries. PURPOSE: The purpose of this study was to understand the effects of backwards walking on quadriceps muscle activity. METHODS: A single participant who had an ACL reconstruction (F, age: 21 yrs, time since surgery: 33 months) and a single healthy, uninjured control (F, age: 21) completed three walking trials each lasting 2.5 minutes for three conditions: walking at self-selected forward speed (SSF), self-selected backwards speed (SSB), and walking forward at the self-selected backwards speed (BMF). During each walking trial, quadriceps muscle activity was recorded using surface electromyography sensors placed on the rectus femoris, vastus lateralis, and vastus medialis (Myomotion, Noraxon) sampling at 2,000Hz. EMG data were averaged across each step for each condition and normalized to the EMG recorded from the respective muscle during an isometric quadriceps maximal voluntary isometric contraction. RESULTS: Rectus femoris muscle activity was 0.016, 0.034, 0.012 for the ACL leg of the ACL participant and 0.024, 0.043, and 0.021 for the left leg of the healthy participant for SSF, SSB, and BMF trials, respectively. Vastus lateralis muscle activity 0.038, 0.054, and 0.027 for the ACL leg of the ACL participant and 0.028, 0.092, and 0.021 for the left leg of the healthy participant for SSF, SSB, and BMF trials, respectively. Vastus medialis muscle activity was 0.050, 0.099, and 0.033 for the ACL leg of the ACL participant and 0.029, 0.063, and 0.023 for the left leg of the healthy participant for SSF, SSB, and BMF trials, respectively. CONCLUSION: Both participants showed greater quadriceps muscle activity during the self-selected backwards walking trials. Therefore, backwards walking at a self-selected pace could be implemented in rehabilitation programs to improve quadriceps activation after ACL reconstruction.