  Automated biomechanical testing has great potential for the development of VR
applications, as initial insights into user behaviour can be gained in silico
early in the design process. In particular, it allows prediction of user
movements and ergonomic variables, such as fatigue, prior to conducting user
studies. However, there is a fundamental disconnect between simulators hosting
state-of-the-art biomechanical user models and simulators used to develop and
run VR applications. Existing user simulators often struggle to capture the
intricacies of real-world VR applications, reducing ecological validity of user
predictions. In this paper, we introduce SIM2VR, a system that aligns user
simulation with a given VR application by establishing a continuous closed loop
between the two processes. This, for the first time, enables training simulated
users directly in the same VR application that real users interact with. We
demonstrate that SIM2VR can predict differences in user performance, ergonomics
and strategies in a fast-paced, dynamic arcade game. In order to expand the
scope of automated biomechanical testing beyond simple visuomotor tasks,
advances in cognitive models and reward function design will be needed.
