The use of immersive virtual reality (VR) technologies for ergonomic assessment is gaining increasing relevance as digital tools become integral to human-centered design processes. However, questions remain regarding the reliability and representativeness of postural evaluations conducted in virtual environments compared to those performed in the real world. This study explores the effectiveness of virtual ergonomic analysis by applying a structured, sensor-based protocol to two manual assembly tasks executed in both real and virtual settings. Full-body motion capture and the RULA method were employed to objectively assess postural risk, with consistent task sequences and workstation setups ensuring comparability across conditions. By analyzing and comparing results from both environments, the study provides insights into the strengths and current limitations of VR-based ergonomic evaluations. Findings indicate that immersive VR is a promising tool for early-stage ergonomic analysis. Nevertheless, limitations emerged in tasks involving high physical demands or requiring precise manual alignment, where the absence of physical feedback in VR may lead to an underestimation of postural risk. These observations underscore the need to improve interaction fidelity to enhance the validity and applicability of VR-based ergonomic assessments in industrial contexts.