Biohybrid actuators leveraging living muscle tissue offer the potential to replicate natural motion for biomedical and robotic applications. However, challenges such as limited force output and inefficient force transfer at tissue interfaces persist. The myotendinous junction, a specialized interface connecting muscle to the tendon, plays a critical role in efficient force transmission for movement. Engineering muscle-tendon units in vitro is essential for replicating native musculoskeletal functions in biohybrid actuators. Here, we present a three-dimensionally bioprinted system integrating skeletal muscle tissue with tendon-mimicking anchors containing fibroblasts, forming a biomimetic interdigitated myotendinous junction. Using computational models, we optimized muscle geometries to enhance deformation and force generation. The engineered system improved mechanical stability, myofiber maturation, and force transmission, generating contractile forces of up to 350 micronewtons over a 3-month period. This work highlights how biomimetic designs and mechanical optimization can advance bioactuator technologies for applications in medicine and robotics.