Physical rehabilitation practiced in the intensive care unit (ICU) is a complex therapeutic interaction between healthcare professionals and patients, delivered in an equally complex environment. Landmark data from two randomised controlled trials (RCTs) of physical rehabilitation interventions delivered in the ICU suggested the potential of these therapies for improving patient outcomes [[5]]. Some "positive" physical rehabilitation trials measured outcomes such as physical function at ICU or hospital discharge, with a direct temporal relationship to the ICU-based intervention [[1]]. Subsequent trials, delivering physical rehabilitation at various stages within the ICU, following ICU, and hospital discharge, showed mixed results, highlighting the methodological nuances of designing and evaluating complex rehabilitation interventions. [Extracted from the article]