Introduction: Practice guidelines recommend early physical therapy in intensive care units (ICU). Feasibility, safety and efficacy are confirmed by growing evidence-based data. Purpose: To perform a qualitative systematic literature review on early exercise in ICUs, focused on the subject areas of "how to do", "for which patients" and "for what benefits". Methods: Articles were obtained from the PubMed, Google Scholar, Physiotherapy Evidence Database (PEDro), Embase, CINAHL, CENTRAL, Cochrane and ReeDOC databases. The full texts of references selected according to title and abstract were read. Data extraction and PEDro scoring were performed. Consort recommendations were used for the drafting of the systematic review, which was declared on the Prospero website. Results: We confirm the feasibility and safety of early exercise in the ICU. Convergent evidence-based data are in favour of the efficacy of early exercise programs in ICUs. But the potential benefit of earlier program initiation has not been clearly demonstrated. Our analysis reveals tools and practical modalities that could serve to standardize these programs. The scientific literature mainly emphasizes the heterogeneity of targeted populations and lack of precision concerning multiple criteria for early exercise programs. Conclusion: Changes in the professional culture of multidisciplinary-ICU teams are necessary as concerns early exercise. Physical therapists must be involved and their essential role in the ICU is clearly justified. Although technical difficulties and questions remain, the results of the present qualitative review should encourage the early and progressive implementation of exercise programs in the ICU. (C) 2015 Societe francaise d'anesthesie et de reanimation (Sfar).