University of Tehran Press Journal of Computational Applied Mechanics 2423-6713 57 3 2026 06 01 The intricate link between anterior cruciate ligament rupture and lower limb muscle fatigue: Musculoskeletal Modeling 514 525 107347 10.22059/jcamech.2026.409534.1765 EN Zeynab Saghaeinooshabadi School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran Mohammad Reza Zakerzadeh School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran 0000-0001-5495-3630 Moahammad Ali Nazari School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran Université Grenoble Alpes, CNRS, Grenoble INP, TIMC, Grenoble, France 0000-0002-7473-2082 Journal Article 2026 01 06 Objective Anterior Cruciate Ligament (ACL) rupture can independently affect an individual’s quality of life. This impact becomes more significant when fatigue and intense activity are involved. The aim of this study is to investigate the muscle forces generated in various muscles of the healthy and injured leg using musculoskeletal modeling in OpenSim software.<br />Methods In this study, a participant with unilateral ACL rupture was asked to perform a one-hour walking protocol. Kinematic data were recorded using reflective markers and motion capture cameras, while kinetic data were collected via force plates. These data were used to model the gait and calculate muscle forces in different leg muscles using full inverse analysis workflow.<br />Results Notable differences were observed in muscle forces between the healthy and injured legs. These differences were particularly evident in the Semimembranosus, Soleus and Gracilis muscles. The Vastus Medialis and Vastus Intermedius of the injured leg produced up to 30% more force compared to the corresponding muscles in the healthy leg during the gait cycle, while the Soleus muscle in the healthy leg generated 47% to 74% greater force Relative to the contralateral limb. The Gracilis muscle also showed more than 45% difference in force production favoring the injured leg.<br />Conclusion Dynamic musculoskeletal modeling was used as a more comprehensive method than surface electromyography for assessing different muscles even deep muscles in patients with musculoskeletal disorders. The results agree with EMG study for Vastus Medialis, Gastrocnemius Lateralis and Soleus. Gastrocnemius Medialis showed an approximate agreement with IEMG (Integrated Electro MyoGraphy) results. The behavior of the other surface muscles does not comply with IEMG results. This shows that a better modeling which includes the ligaments is needed. https://jcamech.ut.ac.ir/article_107347_ee908dea22d1d147d8619bd55f41b03a.pdf