A narrative review of qualitative studies on Lean Six Sigma practitioners in Industry 4.0 environment

Purpose The synergy of Lean Six Sigma and Industry 4.0 is reshaping the quality management landscape, driven by the emergence of sophisticated technologies such as artificial intelligence, the Internet of Things, automation and cloud computing. While the existing studies have extensively documented the technical and operational gains from this shift, there is still a critical gap in understanding how these changes are experienced by Lean Six Sigma practitioners. This study aims to address that gap by conducting a qualitative synthesis of related journals that examine the human side of Lean Six Sigma and Industry 4.0 integration, particularly within the define, measure, analyze, improve and control (DMAIC) problem-solving discipline. Design/methodology/approach Anchored in an interpretivist paradigm, the review applies a bottom-up thematic analysis using NVivo software to extract, categorize and conceptualize practitioner experiences. The coding process progressed inductively from study-level findings to code clusters, which were then grouped into categories and synthesized into broader themes. Findings The synthesis reveals four recurring themes across the reviewed qualitative studies: (1) the evolving role of Lean Six Sigma practitioners in digitally enabled environments, (2) uneven integration of Industry 4.0 technologies across the DMAIC phases, with stronger emphasis on measure, analyze and control, (3) persistent challenges and enabling conditions shaping adoption and (4) critical success factors related to leadership, culture, infrastructure and integration frameworks. The findings further indicate that existing research predominantly emphasizes technical and operational benefits, while practitioner experiences, organizational sense-making and human adaptation remain insufficiently explored. Methodologically, the literature is dominated by single-site case studies and short-term analyses, with limited use of reflexive, longitudinal or theory-informed qualitative designs. Originality/value Finally, this paper positions qualitative synthesis as not merely complementary to quantitative performance metrics but essential for understanding the deeply situated, lived experiences that define transformation at the frontline. It calls for a human-centered, reflexive and theory-informed research agenda that can bridge the current disconnect between abstract digital frameworks and reality for Lean Six Sigma practitioners in the age of digital transformation.