Objective The muscle force characteristics of the knee joint during the roundhouse kick in Taekwondo is explored. Methods Using the DaeDo electronic scoring system, Vicon optical motion capture system, and Kistler three-dimensional force plates, we collected kinematic and dynamic data from 12 elite Taekwondo athletes. The OpenSim software was used to simulate these movements and calculate muscle forces, joint torques, joint stiffness, and muscle coordination patterns of the knee joints. Results For the attacking leg, the coronal axis torque at the knee joint was significant during the knee-lifting and recovery moments, showing similar values, while the sagittal axis torque peaked during the striking moment. The vertical axis torque increased slightly at the striking moment compared to the preparation moment, indicating a stable trend. For the supporting leg, the coronal axis torque was highest during the knee-lifting moment, the sagittal axis torque peaked at the striking moment, and the vertical axis torque was highest at the preparation moment. High joint stiffness observed in both legs during the knee-lifting moment could potentially lead to injuries of joint structures such as the ACL. In terms of muscle forces, muscles like the semimembranosus and semitendinosus of the attacking leg reached their peak forces during the striking moment, whereas the supporting leg showed greater forces during the recovery phase. Additionally, four patterns of muscle coordination were identified, demonstrating complex neuromuscular coordination during the roundhouse kick motion. Conclusions During the knee-lifting and striking phases, the coronal axis torque of the knee joint in the attacking leg is significant, while the sagittal axis torque peaks at the moment of strike. For the supporting leg, the highest coronal axis torque of the knee joint occurs during knee lifting, with the sagittal axis torque reaching its peak during the strike. In terms of muscle activity, the semimembranosus and the long head of the biceps femoris in the attacking leg exert greater force during the striking phase, whereas the semimembranosus and the medial head of the gastrocnemius in the supporting leg are more active during the recovery phase. There are four cooperative muscle patterns present in the action of a taekwondo backside kick.