EMG Evaluation of Bodyweight Exercise Progression in a Validated ACL Injury Rehabilitation Program: Cross-sectional Study Objectives Regaining muscle strength is essential for successful outcome after anterior cruciate ligament (ACL) injury, why progression of exercise intensity in ACL injury rehabilitation is important. Thus, this study evaluated hamstring and quadriceps muscle activity progression during bodyweight exercises used in a validated ACL injury rehabilitation program. Design The study design involved single-occasion repeated measures in a randomized manner. Twenty healthy athletes (nine females) performed nine bodyweight exercises (three exercises per rehabilitation phase). Surface electromyography signals were recorded for hamstring (semitendinosus, biceps femoris) and quadriceps (vastus medialis, vastus lateralis) muscles, and normalized to isometric peak EMG (nEMG). Results Hamstring muscle activity did not increase from one rehabilitation phase to the next, ranging between 8-45% nEMG for semitendinosus and 11-54% nEMG for biceps femoris. Only one exercise (Cook hip lift) exhibited hamstring muscle activities above 60% nEMG. By contrast, quadriceps muscle activity increased, and late phase exercises displayed high nEMG (vastus lateralis >60% and vastus medialis >90% nEMG). Conclusion The examined bodyweight exercises did not progress for hamstring muscle activity but successfully progressed for quadriceps muscles activity. This study highlights the need for consensus on exercise selection when targeting the hamstring muscles in the rehabilitation after ACL injury. This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. Conflicts of interest None declared. Funding None declared. Corresponding author: Mette Kreutzfeldt Zebis E-mail corresponding author: mzeb@kp.dk Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.